Remove deleted versions from builds queue

Stupid mistake! Was so focused on ensuring deleted versions were skipped
in current builds, and ignored in future refreshes of the build_queue
that I forgot to tell slave-driver to eliminate them from the *existing*
build_queue...

piwheels/master/slave_driver.py

@@ -262,6 +262,12 @@ def handle_delete(self, queue):
         for abi in self.excluded_builds:
             self.excluded_builds[abi][(del_pkg, del_ver)] = (
                 datetime.now(tz=UTC) + timedelta(hours=1))
+        for abi, build_queue in self.abi_queues.items():
+            self.abi_queues[abi] = [
+                (pkg, ver)
+                for pkg, ver in build_queue
+                if (del_pkg, del_ver) not in ((pkg, ver), (pkg, None))
+            ]
         for slave in self.slaves.values():
             if slave.reply[0] == 'BUILD':
                 build_pkg, build_ver = slave.reply[1]