Libretro: Remove serial emulation workaround

These are not needed anymore due to previous 2 commits.

src/libretro/Makefile

@@ -2,7 +2,7 @@ DEBUG=0
 TILED_RENDERING=0
 STATIC_LINKING=0
 FRONTEND_SUPPORTS_RGB565=1
-NO_LINK=0
+NO_LINK=1
 
 SPACE :=
 SPACE := $(SPACE) $(SPACE)

src/libretro/libretro.cpp

@@ -92,72 +92,6 @@ void (*dbgOutput)(const char* s, uint32_t addr);
 void (*dbgSignal)(int sig, int number);
 #endif
 
-// Dummy vars/funcs for serial io emulation without LINK communication related stuff
-#ifndef NO_LINK
-#include "../gba/GBALink.h"
-uint8_t gbSIO_SC;
-bool LinkIsWaiting;
-bool LinkFirstTime;
-bool EmuReseted;
-int winGbPrinterEnabled;
-bool gba_joybus_active = false;
-
-#define UPDATE_REG(address, value) WRITE16LE(((uint16_t*)&ioMem[address]), value)
-
-LinkMode GetLinkMode()
-{
-    return LINK_DISCONNECTED;
-}
-
-void StartGPLink(uint16_t value)
-{
-    if (!ioMem)
-        return;
-
-    UPDATE_REG(COMM_RCNT, value);
-}
-
-void LinkUpdate(int ticks)
-{
-}
-
-void StartLink(uint16_t siocnt)
-{
-/*    log("'s' siocnt = %04x\n", siocnt); */
-
-    if (!ioMem)
-        return;
-
-    if(siocnt & 0x80)
-    {
-        siocnt &= 0xff7f;
-        if(siocnt & 1 && (siocnt & 0x4000))
-        {
-            UPDATE_REG(COMM_SIOCNT, 0xFF);
-            IF |= 0x80;
-            UPDATE_REG(0x202, IF);
-            siocnt &= 0x7f7f;
-        }
-    }
-    UPDATE_REG(COMM_SIOCNT, siocnt);
-}
-
-void CheckLinkConnection()
-{
-}
-
-void gbInitLink()
-{
-   LinkIsWaiting = false;
-   LinkFirstTime = true;
-}
-
-uint16_t gbLinkUpdate(uint8_t b, int gbSerialOn) //used on external clock
-{
-   return (b << 8);
-}
-#endif
-
 #define GS555(x) (x | (x << 5) | (x << 10))
 uint16_t systemGbPalette[24] = {
     GS555(0x1f), GS555(0x15), GS555(0x0c), 0,