scripts/update-linux-headers.sh: Remove temporary directory inbetween

scripts/update-linux-headers.sh: Remove temporary directory inbetween

We are reusing the same temporary directory for installing the headers
of all targets, so there could be stale files here when switching from
one target to another. Make sure to delete the folder before installing
a new set of target headers into it.

Message-ID: <20240527060243.12647-1-thuth@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>