ipk: Fix clean up of extracted IPK payload

It turns out that the IPK payload tarball was actually cleaned up in the
concrete package manager implementation (most likely because at some
point Debian and IPK packages used different compression algorithms).

Globbing removes this ambiguity so move the removal of the payload into
the common extract method.

Signed-off-by: Philip Lorenz <philip.lorenz@bmw.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>