This includes:
- all references to the 3 attachment preview columns in the Gmail
conversation table (except for migration code in MailStoreInitializer)
- all layout and drawing code for attachment previews in conversation list
- all assets related to attachment previews
- all preference and analytics code that aided attachment previews
NOTE: This does not alter, in any way, the display of attachments in
conversation view.
Change-Id: Iccefd2fcf146ccdad927e7911900f370baaf8a1d
a546307c1d