Tidy root of our Git repo: move generate-languages-list to auto/scripts

generate-languages-list is not meant to be used directly
by anyone, so let's move it out of the way.
auto/build has auto/scripts/ in its $PATH.

auto/build

@@ -118,7 +118,7 @@ export MKSQUASHFS_OPTIONS
 ./refresh-translations || fatal "refresh-translations failed ($?)."
 
 # generate list of supported languages
-./generate-languages-list || fatal "generate-languages-list failed ($?)."
+generate-languages-list || fatal "generate-languages-list failed ($?)."
 
 BUILD_ISO_FILENAME="${BUILD_BASENAME}.iso"
 BUILD_MANIFEST="${BUILD_BASENAME}.build-manifest"