libcrc32c: remove crc32c_impl

This was only ever used by btrfs, and the usage just went away.
This effectively reverts df91f56a ("libcrc32c: Add crc32c_impl
function").
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

include/linux/crc32c.h

@@ -5,7 +5,6 @@
 #include <linux/types.h>
 
 extern u32 crc32c(u32 crc, const void *address, unsigned int length);
-extern const char *crc32c_impl(void);
 
 /* This macro exists for backwards-compatibility. */
 #define crc32c_le crc32c

lib/libcrc32c.c

@@ -65,12 +65,6 @@ static void __exit libcrc32c_mod_fini(void)
 	crypto_free_shash(tfm);
 }
 
-const char *crc32c_impl(void)
-{
-	return crypto_shash_driver_name(tfm);
-}
-EXPORT_SYMBOL(crc32c_impl);
-
 module_init(libcrc32c_mod_init);
 module_exit(libcrc32c_mod_fini);