Make SKC#setInputMethodEnabled() consistent among users

With this CL

  AccessibilityService
      .SoftKeyboardController#setInputMethodEnabled()

uses the same logic no matter whether the target userId is

  InputMethodManagerService#mCurrentUserId

or not in favor of better consistency and simplicity.

Overall we do not expect any app compat issues.

Bug: 350386877
Flag: EXEMPT refactor
Test: atest CtsAccessibilityServiceTestCases:AccessibilitySoftKeyboardTest
Change-Id: Ia6765333323523e14c335e1bf38b43190acb5aae