Remove old change screen

The following code was removed:

UI:

  * ChangeScreen (1)
  * SideBySide (1)
  * NewChangeScreenBar

Database columns in the accounts table:

  * change_screen
  * reverse_patch_set_order
  * comment_visibility_strategy

Change-Id: I7ec4a0beb51dd6cb2f7c364df40e7cb5bea786d2
60 files changed