docs/precommit.md: remove broken reference
docs/precommit.md: remove broken reference

Change-Id: Iee012b0c2d6d3ff754288873e7d6508c836befaf
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/694435
Reviewed-by: Julie Qiu <e6cb64861edcc38971590ff27c111e0e672de045@google.com>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite