remove mips support and bots

The NDK has deprecated mips and mips64:
https://developer.android.com/ndk/guides/abis.html

Might as well clean this up now while I remember.

Change-Id: Ie4b2334c75208082067cc16fe355d0349c7e0904
Reviewed-on: https://skia-review.googlesource.com/80560
Reviewed-by: Derek Sollenberger <djsollen@google.com>
12 files changed