[cleanup] precommit checks precommit.sh now checks license headers. install_precommit.sh installs precommit.sh to .git/ license_exemptions.sh defines a function that says whether a file needs a license header. Bug: 445730006 Change-Id: Idb30e023ac4303a6a11ac44ff9ca49c5345ef7ec Reviewed-on: https://fuchsia-review.googlesource.com/c/rsclient/+/1372944 Reviewed-by: James Robinson <jamesr@google.com> Commit-Queue: David Fang <fangism@google.com>