drm/nouveau: Remove file nouveau_fbcon.c

Commit 4a16dd9d ("drm/nouveau/kms: switch to drm fbdev helpers")
converted nouveau to generic fbdev emulation. The driver's internal
implementation later got accidentally restored during a merge commit.
Remove the file from the driver. No functional changes.

v2:
	* point Fixes tag to merge commit (Alex)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Fixes: 4e291f2f ("Merge tag 'drm-misc-next-2022-11-10-1' of git://anongit.freedesktop.org/drm/drm-misc into drm-next")
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: nouveau@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20230110123526.28770-1-tzimmermann@suse.de