v4l2dec: also remove the colorimetry/chroma-site fields from the acquired caps

On acquire_caps() the format of the v4l2 capture plane has been configured by the driver/v4l2 and we are attempting to possibly change that format based on what the downstream supports. Removing only the format from the caps possibly has the effect of producing an invalid format/colorimetry/chroma-site combination when intersecting RGB and YUV formats. Remove all of the format, colorimetry and chroma-site fields so that the caps negotiation with downstream can choose an appropriate format/colorimetry/chroma-site combination.