drm/omapdrm: Nuke omap_framebuffer_get_next_connector()

omap_framebuffer_get_next_connector() uses plane->fb which we want to
deprecate for atomic drivers. As omap_framebuffer_get_next_connector()
is unused just nuke the entire function.

Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180405151400.11326-11-ville.syrjala@linux.intel.com


Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>