scripts/build-distribution-suite: clean up before creating disk images

We don't have unlimited space on the build vm.. these directories might
take about 70 gig for the makerstick, so tidy a bit. Otherwise:

> grub-install: error: cannot copy
> `/usr/share/locale/ca/LC_MESSAGES/grub.mo' to
> `/tmp/stick-install.OMmZ/efiboot/boot/grub/locale/ca.mo': Input/output
> error.
> [ 🛑 ] Sorry, something went wrong.
> [ 🛑 ] Problem occurred in install/hooks/20-install_grub.sh

scripts/build-distribution-suite

@@ -19,7 +19,10 @@ for VARIANT in ${VARIANTS}
 do
     # build variant iso:
     print_info "${COLOR_YELLOW}building ${VARIANT}${COLOR_OFF}"
-    scripts/build-live-iso "${VARIANT}"
+    scripts/build-live-iso "${VARIANT}" \
+        && print_info "${COLOR_YELLOW}Built ok, removing build cruft${COLOR_OFF}" \
+        && du -sh build/chroot build/binary \
+        && rm -r build/chroot build/binary
 
     # build distribution image:
     IMAGE_NAME=$(bash -c 'source scripts/functions.bash && cd build && get_image_name')