Make "ime {enable,disable} --user <userId>" consistent among users

With this CL

  adb shell ime enable --user <userId> <imeId>
  adb shell ime disable --user <userId> <imeId>

start behaving in the same manner across users, meaning that there is
no special behavior when the userId is not IMMS#mCurrentUserId.

No impact is expected on all the tests and manual work in this CL.

Bug: 350386877
Bug: 350834650
Test: manually verified
Flag: EXEMPT refactor
Change-Id: I9efbba6590ae0b586f2e90ab5125da0ad010f7cc