Remove the resetting of qp params for temporal layers.

The ambient qp and active worse/best qp were reset for every frame
when temporal layers is on. This change removes this reset.

As this affects the target size for forced key frames
(it will actually lower the size somewhat), we increased the
inital boost factor to compensate.

Change-Id: Ie38d95f5c99ab3d447469c49e2177bc3fcc4ad28