Previously, I assumed that SDR contents must be BT709, and HDR contents must be
BT2020. Turns out BT2020 is just wide-gamut, and SDR contents / transfers may be
represented in BT2020 color spaces.
Relax the check, so that we don't throw when valid BT2020 SMPTE 170M contents
are input into effects.
PiperOrigin-RevId: 526668347
