.github/workflows: drop FreeBSD tests

This is unfortunate, but without a live platform to test on,
I can't investigate issues, and CI is now failing with just

   ?   	filippo.io/age/cmd/age-keygen	[no test files]
  Killed

which really could be anything.

.github/workflows/test.yml

@@ -22,23 +22,6 @@ jobs:
           fetch-depth: 0
       - name: Run tests
         run: go test -race ./...
-  freebsd:
-    name: Test (FreeBSD)
-    runs-on: macos-12
-    steps:
-      - name: Checkout repository
-        uses: actions/checkout@v2
-        with:
-          fetch-depth: 0
-      - name: Run tests
-        # Unpinned Action allowed with read-only permissions.
-        uses: vmactions/freebsd-vm@v0
-        with:
-          prepare: |
-            freebsd-version
-            pkg install -y go
-            go version
-          run: go test -buildvcs=false -race ./...
   gotip:
     name: Test (Go tip)
     strategy: