update/release: clean up temporary crossgcc dir

clean it up after copying the tarballs

i really hate how this logic is written, it's clunky
but it should work; the only issue is that it's quite
slow, and inefficient on use of disk space.

however, i've not yet figured out how to reproducible
add files to a tarball, once the tarball has been created,
and i rely on sorting (of file names) when creating them.

it's really not a problem because normal people won't
use this script, only i or anyone who wants to test out
the libreboot release infrastructure. this script is
largely intended to *work*

but i'm still annoyed by how crappy it is. i'll fix it
after the Libreboot 20231021 release.

Signed-off-by: Leah Rowe <leah@libreboot.org>

script/update/release

@@ -84,6 +84,7 @@ build_release()
 		    "${srcdir}/src/coreboot/${_xgcc##*/}/util/crossgcc/tarballs" \
 		    || err "!move xgcc tarballs to ${srcdir}/xgcc/${_xgcc##*/}"
 	done
+	rm -Rf "${vdir}/crossgcc" || err "!rm -Rf \"${vdir}/crossgcc\""
 	(
 	cd "${srcdir%/*}" || err "${_xm}: mktarball \"${srcdir}\""
 	mktarball "${srcdir##*/}" "${srcdir##*/}.tar.xz" || err "${_xm}: mksrc"