ci: don't run unit tests on pypy

We never really supported pypy - the CI was running the tests there
just to see compatibility.
A few of the unit tests consistently hang, resulting in the whole
test runner timing out and wasting compute resources. Someone could
debug the hangs and try to fix them, but I don't have the time.

.cirrus.yml

@@ -24,12 +24,6 @@ task:
            # enable additional checks:
            PYTHONASYNCIODEBUG: "1"
            PYTHONDEVMODE: "1"
-    - name: Tox PyPy
-      allow_failures: true
-      env:
-        ELECTRUM_IMAGE: pypy:3
-        TOXENV: pypy3
-        ELECTRUM_PYTHON_NAME: pypy3
   pip_cache:
     folder: ~/.cache/pip
     fingerprint_script: echo $ELECTRUM_IMAGE && cat $ELECTRUM_REQUIREMENTS_CI && cat $ELECTRUM_REQUIREMENTS