vo_corevideo: don't set colormatrix on direct rendering path

The current code uses GL_YCBCR_422_APPLE texture format. This allows to handle
transparently the conversion to RGB but always use BT.601 colormatrix [1].

Hopefully I can adapt gl_video to take CVPixelBuffers soon so that `vo=opengl`
can be used instead of `vo=corevideo` with `hwdec=vda`

 [1]: http://www.opengl.org/registry/specs/APPLE/ycbcr_422.txt
      http://www.opengl.org/registry/specs/APPLE/rgb_422.txt
vo_corevideo: convert to use reconfig instead of config