Fix incorrect path in Mjolnir uninstallation tasks

roles/matrix-synapse/tasks/ext/mjolnir-antispam/setup_uninstall.yml

@@ -2,5 +2,5 @@
 
 - name: Ensure mjolnir-antispam doesn't exist
   file:
-    path: "{{ matrix_synapse_ext_path }}/mjolnir-antispam"
+    path: "{{ matrix_synapse_ext_path }}/mjolnir"
     state: absent