drm/vmwgfx: Remove vmwgfx_hashtab

The vmwgfx driver has migrated from using the hashtable in vmwgfx_hashtab
to the linux/hashtable implementation. Remove the vmwgfx_hashtab from the
driver.

Signed-off-by: Maaz Mombasawala <mombasawalam@vmware.com>
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Reviewed-by: Zack Rusin <zackr@vmware.com>
Signed-off-by: Zack Rusin <zackr@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221022040236.616490-12-zack@kde.org