drm/bochs: Remove manual format test from fb_create

An updated implementation of drm_gem_fb_create() already tests the
driver's planes for supported formats. [1] No need to duplicate this
test in bochs.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://elixir.bootlin.com/linux/v6.9/source/drivers/gpu/drm/drm_gem_framebuffer_helper.c#L169

 # 1
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240902105546.792625-2-tzimmermann@suse.de