fs/pipe: remove buggy and unused 'helper' function

While looking for incorrect users of the pipe head/tail fields (see
commit c27c66a: "fs/pipe: Fix pipe_occupancy() with 16-bit
indexes"), I found a bug in pipe_discard_from() that looked entirely
broken.

However, the fix is trivial: this buggy function isn't actually called
by anything, so let's just remove it ASAP.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: torvalds

include/linux/pipe_fs_i.h

@@ -281,15 +281,6 @@ static inline bool pipe_buf_try_steal(struct pipe_inode_info *pipe,
 	return buf->ops->try_steal(pipe, buf);
 }
 
-static inline void pipe_discard_from(struct pipe_inode_info *pipe,
-		unsigned int old_head)
-{
-	unsigned int mask = pipe->ring_size - 1;
-
-	while (pipe->head > old_head)
-		pipe_buf_release(pipe, &pipe->bufs[--pipe->head & mask]);
-}
-
 /* Differs from PIPE_BUF in that PIPE_SIZE is the length of the actual
    memory allocation, whereas PIPE_BUF makes atomicity guarantees.  */
 #define PIPE_SIZE		PAGE_SIZE