Remove an obsolete comment

This is a follow up CL to our previous CL [1], where we forgot to
remove an obsolete comment, which was dded in our previous attempt to
tackle IME focus handling in InputMethodManager [2].  As the line
mentioned in that CL is now gone, there is no reason to keep that
stale comment.

There should be no behavior change in this CL.

 [1]: Ib455704fe1e9d243f93190a84f230210dbceac2a
      970d9d2e
 [2]: I219394178e4172bc47864297f1418e677dba25e5
      5f05965f

Bug: 141738570
Test: atest CtsInputMethodTestCases CtsInputMethodServiceHostTestCases
Change-Id: Iee92a7eb4dfcfb059b0e1fc105f78dd9bdecbbfc