drm/i915: Remove weird code from intel_atomic_check_bigjoiner()

drm/i915: Remove weird code from intel_atomic_check_bigjoiner()

There's some weird junk in intel_atomic_check_bigjoiner()
that's trying to look at the old crtc state's bigjoiner
usage for some reason. That code is totally unnecessary,
and maybe even actively harmful. Not entirely sure which
since it's such a mess that I can't actually wrap my brain
around what it ends up doing.

Either way, thanks to intel_bigjoiner_add_affected_crtcs()
all of the old bigjoiner crtcs are guaranteed to be in the
state already if any one of them is in the state. Also if
any one of those crtcs got flagged for a modeset, then all
of them will have been flagged, and the bigjoiner links
will have been detached via kill_bigjoiner_slave().

So there is no need to look examing any old bigjoiner
usage in intel_atomic_check_bigjoiner(). All we have to care
about is whether bigjoiner is needed for the new state,
and whether we can get the slave crtc we need.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220203183823.22890-4-ville.syrjala@linux.intel.com
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>