Rectify updateFromImpl to handle edge cases better.

The returned value will be true when the app specific configuration is
successfully stored or removed based on the input provided. It will be
false when the the requested configuration is same as the pre-existing
app-specific configuration.

Bug: 204061036

Test: atest WmTests:ActivityTaskManagerServiceTests

Change-Id: I2f528cbadf0e01ed4dba571bb55b19b2b4890231