keys: drop shadowing dead prototype

The global variable pkcs7 does not exist.
Drop the variable declaration, but keep the struct prototype needed for
is_key_on_revocation_list().

Reported by clang:

    ./include/keys/system_keyring.h:104:67: warning: declaration shadows a variable in the global scope [-Wshadow]
      104 | static inline int is_key_on_revocation_list(struct pkcs7_message *pkcs7)
          |                                                                   ^
    ./include/keys/system_keyring.h:76:30: note: previous declaration is here
       76 | extern struct pkcs7_message *pkcs7;
          |                              ^

Fixes: 56c5812 ("certs: Add EFI_CERT_X509_GUID support for dbx entries")
Signed-off-by: Christian Göttsche <[email protected]>
Signed-off-by: Jarkko Sakkinen <[email protected]>

Author: cgzones

include/keys/system_keyring.h

@@ -73,7 +73,6 @@ static inline void __init set_machine_trusted_keys(struct key *keyring)
 }
 #endif
 
-extern struct pkcs7_message *pkcs7;
 #ifdef CONFIG_SYSTEM_BLACKLIST_KEYRING
 extern int mark_hash_blacklisted(const u8 *hash, size_t hash_len,
 			       enum blacklist_hash_type hash_type);
@@ -93,6 +92,7 @@ static inline int is_binary_blacklisted(const u8 *hash, size_t hash_len)
 }
 #endif
 
+struct pkcs7_message;
 #ifdef CONFIG_SYSTEM_REVOCATION_LIST
 extern int add_key_to_revocation_list(const char *data, size_t size);
 extern int is_key_on_revocation_list(struct pkcs7_message *pkcs7);