buildRustCrate: don't try to set CARGO_FEATURE_ variables for dep: features
These features are internal-only, have special characters that bash
doesn't support in variable names, and aren't normally given
environment variables by cargo as far as I can tell.
(cherry picked from commit ede639a8d63f2c6da0944cab441955ca16e9cce5)
(cherry picked from commit a94a643de982df1a1e94fb09fb6bc974def243ef)