Clean up orphan functions and tiny one-off helpers

[teunbrand]

This PR doesn't adress an issue, but I think it is worth to consider anyway.

In essence, it tries to cleanup three types of functions:

1. Orphan functions that were used at some point, but have fallen in disuse because surrounding code has been refactored.
2. Tiny helper functions that are used only once and can easily be used written out in full.
3. Mirror functions where two versions of nearly identical code existed, like the simplify()/simplify_formula() or as.quoted()/as_quoted().