fbdev: omapfb: Drop unused remove function

OMAP2_VRFB is a bool, so the vrfb driver can never be compiled as a
module. With that __exit_p(vrfb_remove) always evaluates to NULL and
vrfb_remove() is unused.

If the driver was compilable as a module, it would fail to build because
the type of vrfb_remove() isn't compatible with struct
platform_driver::remove(). (The former returns void, the latter int.)

Fixes: aa1e49a3 ("OMAPDSS: VRFB: add omap_vrfb_supported()")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Helge Deller <deller@gmx.de>