The user no longer has control over this. Now, the "default" account
(which is only used for prepopulating the name of new accounts is
either the last used account (to be defined), or the first account in
the database.
This removes a setting, and simplifies a lot of code.
We may also want to auto-select the default account when entering the
compose screen from the combined view, but we do not currently have
an easy way to do that.
Bug: 7442992
Change-Id: Iff5bb36d8cbd327334211b670fa4851cbda6b9a0
229c070b0b