exec: Remove reset_files_struct

Now that exec no longer needs to restore the previous value of current->files
on error there are no more callers of reset_files_struct so remove it.
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
v1: https://lkml.kernel.org/r/20200817220425.9389-3-ebiederm@xmission.com
Link: https://lkml.kernel.org/r/20201120231441.29911-3-ebiederm@xmission.comSigned-off-by: Eric W. Biederman <ebiederm@xmission.com>

fs/file.c

@@ -436,18 +436,6 @@ void put_files_struct(struct files_struct *files)
 	}
 }
 
-void reset_files_struct(struct files_struct *files)
-{
-	struct task_struct *tsk = current;
-	struct files_struct *old;
-
-	old = tsk->files;
-	task_lock(tsk);
-	tsk->files = files;
-	task_unlock(tsk);
-	put_files_struct(old);
-}
-
 void exit_files(struct task_struct *tsk)
 {
 	struct files_struct * files = tsk->files;

include/linux/fdtable.h

@@ -108,7 +108,6 @@ struct task_struct;
 
 struct files_struct *get_files_struct(struct task_struct *);
 void put_files_struct(struct files_struct *fs);
-void reset_files_struct(struct files_struct *);
 int unshare_files(void);
 struct files_struct *dup_fd(struct files_struct *, unsigned, int *) __latent_entropy;
 void do_close_on_exec(struct files_struct *);