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

This file was removed in commit 2a1e50d4ccdeb4fc752e2ace8e487a5a17d1e113 but the
uplift 7c2c08c7257fc20c00af2c533f0f04ac8dae1abb didn't remove it. This fixes
this.