[FIX] Remove duplicate getCommonRoomEvents() event binding for pinnedMessages

[aKn1ghtOut]

Checklist

• I have read the Contributing Guide
• I have signed the CLA
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• I have added necessary documentation (if applicable)
• Any dependent changes have been merged and published in downstream modules

Proposed changes

The getCommonRoomEvents() returned functions were bound to the pinnedMessages template twice. This was causing some bugs, as detailed in the Issue mentioned below.

Issue(s)

Closes #19952

Steps to test or reproduce

1. Go to the menu for a channel ('...')
2. Click on 'Pinned Messages'
3. Hover over any pinned message to get the menu ('...') and click on it.
4. Clicking anywhere doesn't do anything because the blocking popover element was created twice by the menu dots button, but only one could be closed.

Further comments

[aKn1ghtOut]

Please have a look :) @dougfabris @ggazzo