Avoid resetting touch to focus in onPreviewStarted for N4

N4 HAL stability issues seem to be exacerbated by resetting focus
in onPreviewStarted. Removing this call yields OK performance for
N4 and removes any repros for the known issue.

Bug: 18681082
Change-Id: I7f78ad648ff55dee412abb18560276cba99ab988
1 file changed