flex_proportions: remove unused fprop_local_single

The single variant of flex_proportions is not used.  Simply remove it.

Link: https://lkml.kernel.org/r/20240118201321.759174-1-shikemeng@huaweicloud.com


Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>