drm/i915: remove leftover for_each_intel_crtc_masked

The last user of for_each_intel_crtc_masked macro was removed in

commit 0a9ab303
Author: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Date:   Tue Apr 21 17:13:04 2015 +0300

    drm/i915: Remove all *_pipes flags from modeset

Get rid of the unused macro.

Cc: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1472126651-13825-1-git-send-email-jani.nikula@intel.com