When Remove Account is disallowed, show dialog

When DISALLOW_MODIFY_ACCOUNT is set by a device admin, and
the user wants to remove an account, show the support dialog
instead of showing the confirm dialog.

To use the O-API DPM.createAdminSupportIntent(), a wrapper
needs to be used, because existing Robolectric tests otherwise
don't compile.

Bug: 37413849
Test: make RunSettingsRoboTests -j40 ROBOTEST_FILTER=*RemoveAccountPreferenceControllerTest

Change-Id: If23ea304ab8b9df1748e6acf3032310843b04780