Remove unused obsolete code from FullScreenMagnificationGestureHandler

Usages were deleted in following commits while ago:
- Ib6a0ad7df56c7d040497d6f352abe3d74c38a49f
- Ie2a782b162b837e9bdc4904a486ed292989f83d8

Bug: None
Test: build, push and try fullscreen magnification with gesture
Flag: EXEMPT rrefactor
Change-Id: Iacdf25d59ef89a069a4b5fbbf6791a2f491ef7c7