Move removeClient to ClientController

Besides moving removeClient to ClientController, this CL also introduce
the ClientControllerCallback to notify other IMF components when a
client is removed.

This is a manual refactoring, no feature flag is needed.

Bug: 314150112
Test: atest CtsInputMethodTestCases CtsInputMethodInstallTestCases
Test: atest FrameworksImeTests FrameworksInputMethodSystemServerTests
Test: atest --host FrameworksInputMethodSystemServerTests_host
Change-Id: I2b90fc06f9c7dabf54974b63525c393d4d822fc2