Stop granting default Contacts permission to IMEs.

This partially reverts the previous commit [1], which allowed special
components to be granted some pre-configured default permissions.

With this CL, we no longer grant Contacts permissions to pre-installed
IMEs.  Rationals are:

  1. Even without this CL, not the all pre-installed IMEs are granted
     Contacts permission by default, because it was done during the boot
     time where InputMethodManagerService is not yet completely
     initialized.  The current behavior is confusing not only for users
     but also for developers.
  2. In almost all the cases, IMEs are supposed to be able to work
     without Contacts permission.  Hence it is not too late to ask users
     to grant the permission to the IME after the initial setup is
     completed.
  3. It is difficult to add new features such as File-Based Encryption
     (FBE) with keeping the current implementation, because currently we
     dynamically call mSettings.setCurrentUserId(userId) just to
     enumerate what IMEs will be enabled for a given user.  Adding
     another condition (whether the user has already unlocked the device
     or not) would make things more complicated.

Note that LatinIME has already support the case where Contacts
permission is not granted by default.  It does not ask users for
anything until Setup-Wizard is completed, and requests Contacts
permission only when the user taps a message in the suggestion strip
that suggests users to use contacts name for typing suggestions.

 [1] If8b8cadbd1980ffe7a6fc15bbb5f54a425f6e8f9
     adc1cf46

Bug: 24756974
Bug: 26743676
Change-Id: Ief2a40b5971b3eb97d765f934d20ce7f2ef25665