Remove redundant calls and correct some comments.

1. Remove first initiation of dataspace in the constructor of
   RequestedLayerState;
2. snapshot->stretchEffect has been set in the approach of
   prepareBasicGeometryCompositionState(), so remove the second call.

Change-Id: I784223ddce80756dc88ec78e8f0deb042e6389db
Signed-off-by: jiayongqiang <jiayongqiang@xiaomi.com>