diff --git a/external/xxh64/xxh64.hpp b/external/xxh64/xxh64.hpp
deleted file mode 100644
index 760f4d89..00000000
--- a/external/xxh64/xxh64.hpp
+++ /dev/null
@@ -1,99 +0,0 @@
-/*
- * Copyright (c) 2015 Daniel Kirchner
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-#ifndef XXH64_HPP
-#define XXH64_HPP
-
-#include <cstdint>
-
-struct xxh64 {
-    static constexpr uint64_t hash (const char *p, uint64_t len, uint64_t seed) {
-        return finalize ((len >= 32 ? h32bytes (p, len, seed) : seed + PRIME5) + len, p + (len & ~0x1F), len & 0x1F);
-    }
-private:
-    static constexpr uint64_t PRIME1 = 11400714785074694791ULL;
-    static constexpr uint64_t PRIME2 = 14029467366897019727ULL;
-    static constexpr uint64_t PRIME3 =  1609587929392839161ULL;
-    static constexpr uint64_t PRIME4 =  9650029242287828579ULL;
-    static constexpr uint64_t PRIME5 =  2870177450012600261ULL;
-
-    static constexpr uint64_t rotl (uint64_t x, int r) {
-        return ((x << r) | (x >> (64 - r)));
-    }
-    static constexpr uint64_t mix1 (const uint64_t h, const uint64_t prime, int rshift) {
-        return (h ^ (h >> rshift)) * prime;
-    }
-    static constexpr uint64_t mix2 (const uint64_t p, const uint64_t v = 0) {
-        return rotl (v + p * PRIME2, 31) * PRIME1;
-    }
-    static constexpr uint64_t mix3 (const uint64_t h, const uint64_t v) {
-        return (h ^ mix2 (v)) * PRIME1 + PRIME4;
-    }
-#ifdef XXH64_BIG_ENDIAN
-    static constexpr uint32_t endian32 (const char *v) {
-        return uint32_t(uint8_t(v[3]))|(uint32_t(uint8_t(v[2]))<<8)
-               |(uint32_t(uint8_t(v[1]))<<16)|(uint32_t(uint8_t(v[0]))<<24);
-    }
-    static constexpr uint64_t endian64 (const char *v)
-    {
-        return uint64_t(uint8_t(v[7]))|(uint64_t(uint8_t(v[6]))<<8)
-               |(uint64_t(uint8_t(v[5]))<<16)|(uint64_t(uint8_t(v[4]))<<24)
-               |(uint64_t(uint8_t(v[3]))<<32)|(uint64_t(uint8_t(v[2]))<<40)
-               |(uint64_t(uint8_t(v[1]))<<48)|(uint64_t(uint8_t(v[0]))<<56);
-    }
-#else
-    static constexpr uint32_t endian32 (const char *v) {
-        return uint32_t(uint8_t(v[0]))|(uint32_t(uint8_t(v[1]))<<8)
-               |(uint32_t(uint8_t(v[2]))<<16)|(uint32_t(uint8_t(v[3]))<<24);
-    }
-    static constexpr uint64_t endian64 (const char *v) {
-        return uint64_t(uint8_t(v[0]))|(uint64_t(uint8_t(v[1]))<<8)
-               |(uint64_t(uint8_t(v[2]))<<16)|(uint64_t(uint8_t(v[3]))<<24)
-               |(uint64_t(uint8_t(v[4]))<<32)|(uint64_t(uint8_t(v[5]))<<40)
-               |(uint64_t(uint8_t(v[6]))<<48)|(uint64_t(uint8_t(v[7]))<<56);
-    }
-#endif
-    static constexpr uint64_t fetch64 (const char *p, const uint64_t v = 0) {
-        return mix2 (endian64 (p), v);
-    }
-    static constexpr uint64_t fetch32 (const char *p) {
-        return uint64_t (endian32 (p)) * PRIME1;
-    }
-    static constexpr uint64_t fetch8 (const char *p) {
-        return uint8_t (*p) * PRIME5;
-    }
-    static constexpr uint64_t finalize (const uint64_t h, const char *p, uint64_t len) {
-        return (len >= 8) ? (finalize (rotl (h ^ fetch64 (p), 27) * PRIME1 + PRIME4, p + 8, len - 8)) :
-               ((len >= 4) ? (finalize (rotl (h ^ fetch32 (p), 23) * PRIME2 + PRIME3, p + 4, len - 4)) :
-                ((len > 0) ? (finalize (rotl (h ^ fetch8 (p), 11) * PRIME1, p + 1, len - 1)) :
-                 (mix1 (mix1 (mix1 (h, PRIME2, 33), PRIME3, 29), 1, 32))));
-    }
-    static constexpr uint64_t h32bytes (const char *p, uint64_t len, const uint64_t v1,const uint64_t v2, const uint64_t v3, const uint64_t v4) {
-        return (len >= 32) ? h32bytes (p + 32, len - 32, fetch64 (p, v1), fetch64 (p + 8, v2), fetch64 (p + 16, v3), fetch64 (p + 24, v4)) :
-               mix3 (mix3 (mix3 (mix3 (rotl (v1, 1) + rotl (v2, 7) + rotl (v3, 12) + rotl (v4, 18), v1), v2), v3), v4);
-    }
-    static constexpr uint64_t h32bytes (const char *p, uint64_t len, const uint64_t seed) {
-        return h32bytes (p, len, seed + PRIME1 + PRIME2, seed + PRIME2, seed, seed - PRIME1);
-    }
-};
-
-#endif /* !defined XXH64_HPP */