Remove all compatibility with pre-2.0 data

* Remove LocalStore (pre-2.0 mail database) and its unit test
* Remove UpgradeAccounts (converted pre-2.0 accounts to Provider)
* Remove FolderMessageList (receiver for pre-1.6 desktop shortcuts)
* Remove "upgrading" paths through LegacyConversions
* Clip out dangling references to everything above

Bug: 3292310
Change-Id: I5654d55a0879b00b05b63055b94651855a8ee3ef
2 files changed