github actions: remove cache (just caused hangs and failures)

.github/workflows/rust.yml

@@ -18,14 +18,6 @@ jobs:
         with:
           toolchain: stable
           override: true
-      - uses: actions/cache@v2
-        with:
-          path: |
-            .cargo_home
-            target
-          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
-      - name: Configure cargo data directory
-        run: echo "::set-env name=CARGO_HOME::$(pwd)/.cargo_home"
       - name: Build
         run: cargo check
       - name: Run tests