This only applies for the main EmailActivity. The compose window still
uses the user-visible setting for "Default account" as the default
account when handling intents like "mailto:" links.
In the future, we should probably just remove that setting, now that we
remember the last account in the reading-email case.
Bug: 4460450
Change-Id: I4b3e7c9e13b7e89320891346383780cd670492ae