We are losing access to CircleCI so remove it. (#142)

The account on which this CI was running is not beinge renewed so turn off
CircleCI by removing the config file. We can resurrect it later if/when we
get access to a different account under which to run.

We have very similar CI running in GitHub actions anyway so it's not the
end of the world; our tests will still run.

.github/workflows/main.yml

@@ -14,7 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-name: Unit test
+name: GitHub CI
 
 on:
   pull_request:
@@ -31,6 +31,8 @@ jobs:
 
     steps:
       - uses: actions/[email protected]
+        with:
+          fetch-depth: 0
 
       - name: set up environment
         run: |