Bug 844029 - remove autogenerated file metadata_scripts.js left over by a previous uplift

This file was removed in commit 2a1e50d4ccdeb4fc752e2ace8e487a5a17d1e113 but the
uplift 9ccab5adc0dda9740927a26dc7648e8a98c7745c didn't remove it. This fixes
this.