Stop including cidmaps.js

In https://github.com/mozilla/pdf.js/commit/b5b94a4af389ef387570cf22662d9fc6bd41417a, i.e. PR #4259, we stopped using cidmaps.js. Despite that, it's still included when PDF.js is built. At almost 0.5 MB (and approx. 7000 lines), this is currently the single largest file in the codebase.
Including such a large file in the builds, when it is not actually used, seems extremely wasteful; hence this patch.

Please note: I purposely didn't remove the actual file, in the event that we want to use it again in the future.