Delete rustfmt submodule

Author: jyn514

.gitmodules

@@ -16,9 +16,6 @@
 [submodule "src/tools/rls"]
 	path = src/tools/rls
 	url = https://github.com/rust-lang/rls.git
-[submodule "src/tools/rustfmt"]
-	path = src/tools/rustfmt
-	url = https://github.com/rust-lang/rustfmt.git
 [submodule "src/tools/miri"]
 	path = src/tools/miri
 	url = https://github.com/rust-lang/miri.git