fix: remove system dependency on python3 (#1415)

Author: novas0x2a

foreign_cc/private/framework/toolchains/macos_commands.bzl

@@ -261,7 +261,7 @@ def replace_symlink(file):
     # as `readlink` is.
     return """\
 if [[ -L "{file}" ]]; then
-  target="$(python3 -c "import os; print(os.path.realpath('{file}'))")"
+  target="$(realpath '{file}')"
   rm "{file}" && cp -a "${{target}}" "{file}"
 fi
 """.format(file = file)