lib/oe/unpack.py: fix uncompressing .gz .bz2 or .xz

lib/oe/unpack.py: fix uncompressing .gz .bz2 or .xz

* Actually, the uncompressed file is written into the source
path instead of the destination path.
* By also removing the source path, this patch should fix this problem.
* An other fix could be to not uncompress to stdout but let gunzip|bunzip2|
xz uncompress directly to the file.

Signed-off-by: Eric Bénard <eric@eukrea.com>
Acked-by: Frans Meulenbroeks <fransmeulenbroeks@gmail.com>
Acked-by: Chris Larson <chris_larson@mentor.com>