vala: Fix on target wrapper buildpaths issue

The on target wrapper contains paths from the host build. Remove them.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 10980ae5)
Signed-off-by: Steve Sakoman <steve@sakoman.com>