drm/vc4: Remove dead vc4_event_pending().

It is no longer used as of commit 34c8ea40 ("drm/vc4: Mimic
drm_atomic_helper_commit() behavior")

Signed-off-by: Eric Anholt <eric@anholt.net>
Link: http://patchwork.freedesktop.org/patch/msgid/20170621185002.28563-4-eric@anholt.net


Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>