fs/exec.c:acct_arg_size(): ptl is no longer needed for add_mm_counter()

acct_arg_size() takes ->page_table_lock around add_mm_counter() if
!SPLIT_RSS_COUNTING. This is not needed after commit 172703b08cd0 ("mm:
delete non-atomic mm counter implementation").

Signed-off-by: Oleg Nesterov <[e-mail]>
Reviewed-by: Matt Fleming <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: KAMEZAWA Hiroyuki <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/exec.c

···
 		return;
 
 	bprm->vma_pages = pages;
-
-#ifdef SPLIT_RSS_COUNTING
 	add_mm_counter(mm, MM_ANONPAGES, diff);
-#else
-	spin_lock(&mm->page_table_lock);
-	add_mm_counter(mm, MM_ANONPAGES, diff);
-	spin_unlock(&mm->page_table_lock);
-#endif
 }
 
 static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,