remove support for mips64el/loongson3a

We don't have any way to test these, and we do have to
go a little out of our way to maintain these builds.

Change-Id: Ie191ee26753b719f6ee22264d63fbe4252e69bd5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/290840
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
10 files changed