Don't print error messages trying to diff files that have been removed via git rm. Change-Id: Ia0945541208fd7a8362843587f797506000479fc
This replicates the run_tests.sh -8 behavior, running flake8 only on changes made in the last commit and working tree. Change-Id: Iebd5746c78e840225f0860843c77f4c638877c26