Remove git config user.* from GitHub CI

Now that we're using a patched submodule rather than applying patches here, we
don't need to fib to git about identity.

Thanks to David Chisnall for spotting the oversight.

.github/workflows/compile.yml

@@ -20,9 +20,6 @@ jobs:
         submodules: true
     - name: Build simulators
       run: |
-        # fake committer details to satisfy git am
-        git config --global user.name "No One"
-        git config --global user.email "[email protected]"
         eval $(opam env) && make csim
         mkdir install
         cp c_emulator/cheriot_sim install