Remove the appearances.updated_by column which appears to have been

added to schema.rb but was never added in a migration. This has caused
inconsistencies between developer and customer databases and caused
schema.rb to vary from one state and the other over time.

In commit 40104eea the appearances table was added with the updated_by
column but the 20160222153918_create_appearances_ce.rb migration in
commit 9a2869ab never added the updated_by column. As a result the
schema.rb has flipped back and forth several times since as different
developers have checked in schemas with or without this column....

It's not used so let's remove it once and for all.