[native] add yarn clean-rust to native

Summary:
Some build artifacts for native now live in the native_rust_library subdirectory. We should have a yarn script to remove these artifacts, and we should also invoke this script from the yarn clean script.

Related issue: https://linear.app/comm/issue/ENG-2091/android-local-build-failure

Test Plan:
cd native && yarn clean

verified that the target subdirectory was removed

Reviewers: atul, kamil

Reviewed By: atul

Subscribers: ashoat, tomek, abosh

Differential Revision: https://phab.comm.dev/D5443