snap: Remove QEMU before clone
If you snap in an environment where you previously snapped,
`git clone`ing QEMU will fail. Remove the checkout directory.
Fixes:
@@ -270,6 +270,7 @@ parts:
# download source
qemu_dir=${SNAPCRAFT_STAGE}/qemu
+ rm -rf "${qemu_dir}"
git clone --branch ${branch} --single-branch ${url} "${qemu_dir}"
cd ${qemu_dir}
[ -z "${commit}" ] || git checkout ${commit}
