Do nothing if hideSoftInput is called from not focused client.

IMMS#hideSoftInput calls IMMS#setImeWindowVisibilityStatusHiddenLocked
if it is called from not focused client.  However this function changes
IMS visibility state and also changes the back key indicator wrongly.
IMMS should just ignore IMMS#hideSoftInput from not-focused client.

As a preparation to fix b/20764441, this CL partially reverts
Ife3a8733b1a1bf43b195ecf4b8c5082b6538d0a0 but shouldn't have any
user-visible UX regressions.

Bug: 20764441

Change-Id: I60963f1474457ff37cca85e262460dca8105acff