Remove unused pipes and variables from the codebase

[markmatney]

In reviewing the documentation, I noticed some variables (src/data/books.ts) and pipes (ParseJsonPipe, DerpPipe, ImplodePipe) that do not seem to be used anywhere in the code. Please review and remove these files if they are unused.

Also, in general, please remove any other unused code that you can find, including commented-out lines that no longer serve a purpose, e.g.

// let oldcode = true ? 'this is unnecessary' : 'test';

[Hlopec]

done