Remove codegen-backend config override

This addresses maintainer feedback to keep the codegen-backend setting
as a local-only configuration rather than in the committed repository.

Author: zmr-233

.cargo/config.toml

@@ -14,10 +14,6 @@ rustflags = [
     "-Zshare-generics=n", # =off is also an option, but you're going to increase binary size in doing so.
 ]
 
-# Override parent directory's cranelift backend setting for rust-gpu compatibility
-[profile.dev]
-codegen-backend = "llvm"
-
 [target.'cfg(all())']
 rustflags = [
     # FIXME(eddyb) update/review these lints.