fs: unexport __set_page_dirty

Patch series "remove the implicit .set_page_dirty default".

This series cleans up a few lose ends around ->set_page_dirty, most
importantly removes the default to the buffer head based on if no method
is wired up.

This patch (of 3):

__set_page_dirty is only used by built-in code.

Link: https://lkml.kernel.org/r/20210614061512.3966143-1-hch@lst.de
Link: https://lkml.kernel.org/r/20210614061512.3966143-2-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/buffer.c

@@ -611,7 +611,6 @@ void __set_page_dirty(struct page *page, struct address_space *mapping,
 	}
 	xa_unlock_irqrestore(&mapping->i_pages, flags);
 }
-EXPORT_SYMBOL_GPL(__set_page_dirty);
 
 /*
  * Add a page to the dirty page list.