This is a followup to T153182: now that the updated code is deployed so all inserts specify a value for this column, we can drop the unwanted default. No work is blocked on this, so not setting #blocked-on-schema-change.
This should be able to be done with `ALGORITHM=INPLACE, LOCK=NONE` and shouldn't require a table rebuild, per https://dev.mysql.com/doc/refman/5.6/en/innodb-create-index-overview.html#online-ddl-column-operations.
From the checklist at https://wikitech.wikimedia.org/wiki/Schema_changes:
# **ALTERs to run:** https://gerrit.wikimedia.org/r/c/mediawiki/core/+/322728/8/maintenance/archives/patch-externallinks-el_index_60-drop-default.sql
# **Where to run those changes:** all.dblist
# **When to run those changes:** No time constraint.
# **If the schema change is backwards compatible:** Yes.
# **If the schema change has been tested already on some of the test/beta wikis:** It has been auto-deployed to Beta since 15 May, I believe.
# **if the data should be made available on the labs replicas and/or dumps:** N/A
Schema change progress:
[] s1
** [x] codfw
** [x] eqiad progress T197891#4407014
[] s2
** [x] codfw
** [x] eqiad progress T197891#4403310
[] s3
** [] codfw
** [] eqiad
[] s4
** [x] codfw
** [x] eqiad progress T197891#4408159
[] s5
** [x] codfw
** [x] eqiad progress T197891#4398631
[] s6
** [x] codfw
** [x] eqiad progress T197891#4402329
[] s7
** [x] codfw
** [] eqiad progress T197891#4410831
[] s8
** [x] codfw
** [x] eqiad progress T197891#4410664