Remove a special optimization for a quite rare scenario

This CL effectively reverts the following 3 CLs.

 * Reduce window resizing during IME transition
   I5723f627ce323b0d12bd7b93f5b35fc4d342b50c
   792faa2c

 * Clear the inset of previous IME when necessary
   Ib04967f39b2529251e4835c42e9f99dba2cf43f2
   2977eb7b

 * Make IMS#clearInsetOfPreviousIme() reliable
   Ib567daa009c1139858dccadcfc6a04465ebecf36
   833bdced

The main idea behind the first CL is that the target application can
skil avoid layout resizing if the following two conditions are met.

 A. WindowManagerService (WMS) can remember the last IME's inset until
    the next IME's window is fully shown.
 B. Both the last IME and the new IME have the same inset.

Basically the first CL implements the above A part with an assumption
that some IMEs would do the B part.  However, in reality it is quite
unlikely that two random IMEs have the same inset size.  At the same
time, maintaining this kind of special optimization is getting harder
and harder as more and more use cases and form factors need to be
supported.

Let's remove this optimization given that no one is benefited by it.

Fix: 116492038
Test: atest CtsInputMethodTestCases CtsInputMethodServiceHostTestCases
Test: do not see any noticeable visual difference
Change-Id: I8ffbf9bf7c3a8be54df0ca8eac1a1f041ef7d3c9