Removed irrelevant note for Mac users (bevyengine#2017)

The removed comment talks about something in the file that no longer exists.

.cargo/config_fast_builds

@@ -1,7 +1,7 @@
 # Add the contents of this file to `config.toml` to enable "fast build" configuration. Please read the notes below.
 
 # NOTE: For maximum performance, build using a nightly compiler
-# If you are using rust stable, remove the "-Zshare-generics=y" below (as well as "-Csplit-debuginfo=unpacked" when building on macOS).
+# If you are using rust stable, remove the "-Zshare-generics=y" below.
 
 [target.x86_64-unknown-linux-gnu]
 linker = "/usr/bin/clang"