Account settings: Fix duplicate title and extra padding.

This change reverts the change in
I3981ce73fef63f06a40e61e894481d24284614ba to add a PreferenceCategory
for the accounts after merging the page with autofill settings. That was
done to get the Accounts heading to display for the personal/work
profile view.
This change instead sets the title on the existing PreferenceCategory
that's created dynamically in the Controller.

Removing the extra PreferenceCategory also fixes the padding.

Fix: 183677515
Bug: 183677706
Test: manual - with single profile, with personal/work profiles
Test: make -j RunSettingsRoboTests \
 ROBOTEST_FILTER="com.android.settings.accounts.AccountPreferenceControllerTest"
Change-Id: Ib7fe6f97b93b81d5a5897280cdd6bbad1b75f3a9