Remove local, unused compiler-builtins

Author: crawfxrd

.cargo/config

@@ -18,6 +18,3 @@
 	path = orbclient
 	url = https://gitlab.redox-os.org/redox-os/orbclient.git
 	branch = no_std
-[submodule "compiler-builtins"]
-	path = compiler-builtins
-	url = https://github.com/rust-lang/compiler-builtins.git