Further simplify FINISH_INPUT_NO_FALLBACK_CONNECTION handling

This CL aims to further simplify what MSG_SET_INTERACTIVE handler
needs to do, which was introduced in my previous CL [1].

So redispatching the task to the UI thread is necessary when and only
when "interactive" parameter is true.  If it's false, we can directly
invoke DelegateImpl#finishInputAndReportToIme().

 [1]: I0c95d7e70357ac98b336cd1b51a7405ba92a9a6f

Bug: 234882948
Test: presubmit
Change-Id: I19e14526a094900c80d9c3fc00f576e3a50cafb2