Remove CQ for unsupported branch chrome/m91

Change-Id: I52e1d938a6478bc6ac5ee1b378727df62cf535a3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/447581
Reviewed-by: Heather Miller <hcm@google.com>
Reviewed-by: Eric Boren <borenet@google.com>