PostgreSQL doesn't support anything like this. For now, avoid generating
invalid SQL by just ignoring the option. If we come up with a use case
someday, that can guide implementation of a workalike.
Also, remove a pointless "IGNORE" from populateExternallinksIndex60.php.
el_index_60 isn't uniquely indexed, so it has no effect anyway.
Bug: T215169
Change-Id: I1409c80b39834d1977c82c489226255a8cc93fd0
Adds a maintenance script to populate the field, has that be
automatically run during update.php, and drops the no-longer-needed
default value on the column (where possible: mssql has some sort of
constraint thing going on that I have no idea how it works).
Bug: T59176
Change-Id: I971edf013a1a39466aca3b6e34c915cb24fd3aa7
