Commit cf0eb46afc added this to let
Django understand the CREATE INDEX CONCURRENTLY statement that had
been hidden in a RunSQL query in migration 0244. However, migration
0245 explained that same index to Django in a different way by setting
db_index=True. Move that to 0244 where the index is actually created,
using SeparateDatabaseAndState.
Also remove the part of the SQL in 0245 that was mirrored by dummy
state_operations, and replace it with real operations.
Signed-off-by: Anders Kaseorg <anders@zulip.com>