Remove an unused param from IMMS#showInputMethodPickerFromClient()

This is a follow up CL to our previous CL [1], which introduced

  InputMethodManagerService#showInputMethodPickerFromClient(
          @NonNull IInputMethodClient client,
          int auxiliarySubtypeMode, int displayId);

Somehow the "client" has never been used, which is fine because the
actual caller verification is done by requiring WRITE_SECURE_SETTINGS
permission.

Let's remove such an unused parameter for simplicity.

There must be no observable behavior change.

 [1]: Ic7d7c5a7ad8005a3fbd9d1c1b73e3c5a39a07001
      0b05f9e4

Bug: 234882948
Test: presubmit
Change-Id: I2f27160cbe7d83201c8f52dbb6dcb774a5b8ae43