binfmt: Remove loader from linux_binprm struct

Commit 987f20a ("a.out: Remove the a.out implementation") removed
the last in-tree user of the loader field, and as far as I can tell, it
was the only one historically.

Signed-off-by: Yonatan Goldschmidt <yon.goldschmidt@gmail.com>
Link: https://lore.kernel.org/r/20250223223234.13764-1-yon.goldschmidt@gmail.com
Signed-off-by: Kees Cook <kees@kernel.org>

Author: Jongy

fs/exec.c

@@ -755,8 +755,6 @@ int setup_arg_pages(struct linux_binprm *bprm,
 	mm->arg_start = bprm->p;
 #endif
 
-	if (bprm->loader)
-		bprm->loader -= stack_shift;
 	bprm->exec -= stack_shift;
 
 	if (mmap_write_lock_killable(mm))

include/linux/binfmts.h

@@ -64,7 +64,7 @@ struct linux_binprm {
 	const char *fdpath;	/* generated filename for execveat */
 	unsigned interp_flags;
 	int execfd;		/* File descriptor of the executable */
-	unsigned long loader, exec;
+	unsigned long exec;
 
 	struct rlimit rlim_stack; /* Saved RLIMIT_STACK used during exec. */