cred: remove unused get_new_cred()

This helper is not used anymore so remove it.

Link: https://lore.kernel.org/r/20241125-work-cred-v2-29-68b9d38bb5b2@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

Documentation/security/credentials.rst

@@ -527,11 +527,6 @@ There are some functions to help manage credentials:
      This gets a reference on a live set of credentials, returning a pointer to
      that set of credentials.
 
- - ``struct cred *get_new_cred(struct cred *cred);``
-
-     This gets a reference on a set of credentials that is under construction
-     and is thus still mutable, returning a pointer to that set of credentials.
-
 
 Open File Credentials
 =====================

include/linux/cred.h

@@ -200,19 +200,6 @@ static inline struct cred *get_new_cred_many(struct cred *cred, int nr)
 	return cred;
 }
 
-/**
- * get_new_cred - Get a reference on a new set of credentials
- * @cred: The new credentials to reference
- *
- * Get a reference on the specified set of new credentials.  The caller must
- * release the reference.
- */
-static inline struct cred *get_new_cred(const struct cred *cred)
-{
-	struct cred *nonconst_cred = (struct cred *) cred;
-	return get_new_cred_many(nonconst_cred, 1);
-}
-
 /**
  * get_cred_many - Get references on a set of credentials
  * @cred: The credentials to reference