Remove references of the previous surface control in ViewRootImpl

Partial revert to fix regression from f7645aa9 which
kept a strong ref of the old SC used to detect when the SC changed. This meant that during the lifetime of an app it could keep an additional buffer alive.

Bug: 135762652, 132205507
Test: go/wm-smoke
Test: dumpsys meminfo

Change-Id: I93df8b4ef8ffdded6c46fb44ca4cd110038d75d0