Fix: unnecessary shortcut data and observer setup

KeyGestureController pipeline is active only under flag,
so don't load system shortcuts and bookmarks if KGC flag
is diabled.

Bug: 378584728
Test: atest InputTests
Flag: com.android.hardware.input.use_key_gesture_event_handler
Change-Id: I17f7949b3c4dbfe119a4fd85444cbe5dc3e32c87