Remove macOS Aarch64 target

This target requires cross-compilation on the default (x86_64) `macos-latest`
platform. However, `cross` does [not yet](cross-rs/cross#508)
provide the right target. If tests can be skipped a build solution outside
of `cross` is already discussed [here](BurntSushi/ripgrep#1737).

.github/workflows/test.yml

@@ -29,10 +29,6 @@ jobs:
             target: x86_64-apple-darwin
             use-cross: false
 
-          - os: macos-latest
-            target: aarch64-apple-darwin
-            use-cross: true
-
     steps:
     - name: Checkout repository
       uses: actions/checkout@v2