frameworks/base: some camera-interface cleanup

Methods getNumberOfVideoBuffers() and getVideoBuffer() as well as struct
image_rect_struct are no longer used (instead, the necessary information is
passed through ANativeWindow.)

Change-Id: If4b11446fc9ccbde1f6b45bc70c0d0b8e54376eb
Signed-off-by: Iliyan Malchev <malchev@google.com>