Remove InputMethodSubtypeSwitchingController#mContext

This CL removes

  InputMethodSubtypeSwitchingController#mContext

to simplify UserData initialization process. Removing it also allows
us to remove

  UserDataRepository#mContext,

which was added because of the above dependency [1].

There must be no user observable behavior change.

 [1]: I47c641623aebc6885fa005f4ff688c3786c64e8d
      8fcb843e

Bug: 305849394
Bug: 347693610
Test: presubmit
Flag: EXEMPT refactor
Change-Id: I83ce92143fe0b9ceb5747779f3d192eb8af76ba6