ci: mips is not tier 3, remove CI jobs

Author: seanmonstar

.github/workflows/ci.yml

@@ -120,10 +120,6 @@ jobs:
           - arm-unknown-linux-gnueabi
           - arm-unknown-linux-gnueabihf
           - armv7-unknown-linux-gnueabihf
-          - mips-unknown-linux-gnu
-          - mips64-unknown-linux-gnuabi64
-          - mips64el-unknown-linux-gnuabi64
-          - mipsel-unknown-linux-gnu
           - powerpc-unknown-linux-gnu
           - powerpc64-unknown-linux-gnu
           - powerpc64le-unknown-linux-gnu