build: stop using Python 2.7 in the Mac builder

Remove code in the Mac builder to install Python 2.7 using pyenv. This
no longer works and it is no longer needed by anything.

Signed-off-by: Rafael Kitover <rkitover@gmail.com>

tools/builder/core.sh

@@ -833,11 +833,6 @@ mac_install_core_deps() {
 
     ln -sf "$(find "$BREW_PREFIX"/Cellar/gnu-getopt -path '*/bin/getopt' | head -1)" "$BUILD_ROOT/root/bin/getopt"
 
-    if ! [ -d "$(pyenv root)/versions/2.7.18" ]; then
-        pyenv install -s 2.7.18
-    fi
-    pyenv global  2.7.18
-
     export PATH=$(pyenv root)/shims:$PATH
 
     # This is necessary because someone broke my compiler.