recipetool: create: fix error when extracting source to a specified directory

recipetool: create: fix error when extracting source to a specified directory

Having fetched the source and unpacked it to a temporary directory, we
then move part of it to the destination directory, or if the source is at
the top level we move the whole temporary directory, but in the latter
case we were later attempting to delete the temporary directory which no
longer existed. Clear out the variable so that doesn't happen.

(From OE-Core rev: 91714a52e91cddba5a16c73cf5765d1f47f7856c)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>