Remove TODO comment in IMMS#applyImeVisibliity

As originally the TODO mentioned calling mWindowManagerInternal.hideIme
from IMMS that WM may not know which IME control target should apply
hideIme, since CL[1] has fixed with piping windowToken for hideSoftInput
to WM, so we can simply remove this TODO item.

[1]: Ia596a392eb73ae46debd097151c8c9a7edd59833

Bug: 246309664
Test: atest CtsInputMethodTestCases
Change-Id: I1e76138221bef8687507b4fcb18049d83215b5bf