I don't know why there is hardcoded knowledge of S in the fetcher but there
shouldn't be and the OE unpack changes highlight this doing things it
shouldn't.
Drop the S reference and use rootdir which is the only place it should
be touching.
(Bitbake rev: 84f102954e10a3390fca9c26d5c3c639e952a2c9)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>