ext.echo.overlay: Unbreak removal logic

Apparently three wrongs make a right: hiding the overlay still worked.

* '#pt-notifications a' click event handler was not correctly checking
  for events comig from inside the overlay due to a missing dot before
  class name
  * But if it were correctly checking, it would not be hiding the
    overlay pokey (just its body) due to a copy-paste error
* Instead the clicks were handled by the 'body' click event handler,
  which did not correctly check for events coming from
  '#pt-notifications a'

I made things right again. The user-facing behavior is the same.

Change-Id: I02aba0e25ba4d81b234b327f120e0e2ff13d117c
Merge "ext.echo.overlay: Unbreak removal logic"