Revert "Update dependency etherpad to v2.7.3-0"

This reverts commit 68cc4a1c12.

Etherpad has been reported to be somewhat broken. Broken how? No clue.
Reverting till further feedback comes.

requirements.yml

@@ -27,7 +27,7 @@
   version: 542a2d68db4e9a8e9bb4b508052760b900c7dce6
   name: docker_sdk_for_python
 - src: git+https://github.com/mother-of-all-self-hosting/ansible-role-etherpad.git
-  version: v2.7.3-0
+  version: v2.7.2-1
   name: etherpad
 - src: git+https://github.com/mother-of-all-self-hosting/ansible-role-exim-relay.git
   version: v4.99.1-r0-2-1