netfilter: nf_tables: Remove unused nft_reduce_is_readonly()

Since commit 9e539c5b6d9c ("netfilter: nf_tables: disable expression
reduction infra") this is unused.

Signed-off-by: Yue Haibing <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/net/netfilter/nf_tables.h

···
 #define __NFT_REDUCE_READONLY	1UL
 #define NFT_REDUCE_READONLY	(void *)__NFT_REDUCE_READONLY
 
-static inline bool nft_reduce_is_readonly(const struct nft_expr *expr)
-{
-	return expr->ops->reduce == NFT_REDUCE_READONLY;
-}
-
 void nft_reg_track_update(struct nft_regs_track *track,
 			  const struct nft_expr *expr, u8 dreg, u8 len);
 void nft_reg_track_cancel(struct nft_regs_track *track, u8 dreg, u8 len);