Revert "Only enable rust_toolchain_filegroup targets on Linux hosts"

Revert submission 3462981-rust-toolchain-filegroup

Reason for revert: A simpler solution was implemented in the Rust toolchain build script

Reverted changes: /q/submissionid:3462981-rust-toolchain-filegroup

Change-Id: I0683754690ea81de12949cae611d6d5dc89b0da6
1 file changed