Revert "f2fs: fix to set flush_merge opt and show noflush_merge"

Revert "f2fs: fix to set flush_merge opt and show noflush_merge"

This reverts commit 6ba0594a81f91d6fd8ca9bd4ad23aa1618635a0f which is
commit 967eaad1fed5f6335ea97a47d45214744dc57925 upstream.

Something is currently broken in the f2fs code, Guenter has reported
boot problems with it for a few releases now, so revert the most recent
f2fs changes in the hope to get this back to a working filesystem.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/b392e1a8-b987-4993-bd45-035db9415a6e@roeck-us.net
Cc: Chao Yu <chao@kernel.org>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Yangtao Li <frank.li@vivo.com>
Cc: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>