Remove miri CI stage (#72)

This is temporarily broken.

Author: jsha

.github/workflows/test.yaml

@@ -25,13 +25,3 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - run: cargo fmt -- --check
-
-  miri:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - run: rustup toolchain install nightly
-      - run: rustup default nightly
-      - run: rustup component add miri
-      - run: cargo install xargo
-      - run: cargo +nightly miri test