drm/i915: remove stale comment from sanitize_encoder

This goes back to pre-atomic, where due to intermediate dpms states
connectors and encoder states might indeed not have matched.

With atomic that's all smashed together (and hopefully no bios ever
enables a vga output in dpms standby/suspedn state or we're toast).
In

commit 873ffe69


Author: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Date:   Wed Aug 5 12:37:07 2015 +0200

    drm/i915: Remove connectors_active from sanitization, v2.

sanitize_encoders was changed to disable the encoder in all cases,
which made the comment obsolete.

Remove the misleading comment.

Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171121094241.9129-1-daniel.vetter@ffwll.ch