Inline IMM.DelegateImpl#startInput()

This CL inlines

  InputMethodManager.DelegateImpl#startInput().

There must be no observable behavior change except for we no longer
log IME tracing event

  "InputMethodManager.DelegateImpl#startInput".

If that event is turned out to be useful, we can add a similar tag
later, but for now it doesn't look to be critically useful.

Bug: 234882948
Test: presubmit
Change-Id: I15919fba14c3c78d64796c3e600cfd8f62e73133