ar71xx: base-files: remove the now unneeded 09_fix-seama-header

ar71xx: base-files: remove the now unneeded 09_fix-seama-header

It was intended as a workaround when jffs2 eof mark was included in the
checksum calculation in seama header.  When qihoo-c301 support was
introduced the board name was not inserted into the case list (because I
was not aware of it's existence), but the issue was fixed by excluding
the jffs2 marker as part of the checksum data

Now we are at it, drop it.

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>