Delete invalid records from echo_target_page
Delete invalid records from echo_target_page

Remove the records:

* If a page is no longer valid

* If a notification somehow has been read

* If a notification is no longer a bundle base and has not been removed

Change-Id: I282568691d6649c6e3263aea598c3bba29119a29

wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo