Remove kokoro/format.sh script

We've removed the corresponding kokoro job.

This is a subset of check_format, with the --fix flags instead of --check
flags. It doesn't make sense to run this as part of presubmit or CI.

Bug: 341167730
Change-Id: I492c943bd81c366a19caefb9307ba13e66d19ad0

.github/workflows/ci.yaml

@@ -22,9 +22,6 @@ jobs:
       matrix:
         # Do not add `run-ci` to these commands. We parse them for `xtask run-ci`.
         cmd:
-          # format tries to format all the source files, and relies on the git diff step to determine whether anything was missed.
-          - format
-          # check-format checks for additional issues (e.g. missing license headers) that format does not enforce.
           - check-format
           - run-cargo-deny
           - run-cargo-udeps