Remove maintenance script fixSlaveDesync.php

Remove maintenance script fixSlaveDesync.php

Though this script was run on Wikimedia sites years ago (see T8399), there
are enough reasons to doubt it will be run again:

* There is a hardcoded maximum page_id value, which would have to be
  changed or removed before reuse.
* It scans the entire page table in a single SELECT query and stores all
  values of page_id and page_latest in a PHP array, which might not be
  feasible on a large wiki.
* It writes directly to slaves. In contrast, the manual page for
  pt-table-sync (from Percona Toolkit) says in general, "[...] it always
  makes the changes on the replication master, never the replication slave
  directly. This is in general the only safe way to bring a replica back
  in sync [...]".
* It only works on the page/revision/text tables. In contrast, pt-table-sync
  can work on any table having a primary key.
* It does try to detect whether revisions are missing on the master (instead
  of on the slave). However, this won't work because of a bug introduced in
  r91243 / bb1df74f8715 (it actually queries the master twice and puts the
  second result set in $slaveIDs).

Change-Id: I85c98821af308abf7dde8068d7cbca17d06b1362