remove obsolete presubmit checks

The CQ handles tree closure,
and these {dm,nanobench}_flags.py files don't exist.

Change-Id: I19b5842763efd121a2bf7c3ff9075bf46089d74a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/264342
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed