github/CI: Remove MIPS cross toolchain

MIPS removed by Rust due to rust-lang/rust#115218

Author: sschwarzmann

.github/workflows/lms.yml

@@ -137,7 +137,6 @@ jobs:
           - stable
         target:
           - aarch64-unknown-linux-gnu
-          - mips-unknown-linux-gnu
         features:
           - default