Delete most of IEmailServiceCallback.

The old callback mechanism is being deprecated, and the only
remaining user of this is attachment loading.

In places where the callback was referenced in deprecated
code (e.g. ExchangeService), the code was deleted with no
attempt made to patch it up since the class is unused.

Bug: 9842867

Change-Id: Ia92aa973fe8289759d1b88916d31d86e60a67faa
8 files changed