Add removeInvalidEmails.php maintenance script

The script scans the user table and removes emails
that are technically invalid which don't pass
Sanitizer::validateEmail(), and wouldn't be allowed
today. Confirmed emails are skipped entirely since
they had to be valid at some point.

Bug: T76512
Change-Id: I3cc6396ff6d8b738846b7716b4b0cddc9bf9e1a4
(cherry picked from commit 6002ee6d4bbe64d8623a3696a47c72b9ae431e79)
Merge "Add removeInvalidEmails.php maintenance script" into wmf/1.25wmf10