Simplify Implementation

[eckon]

This project was started at the start of treesitter as a feature of neovim.

It is possible that some of the code is redundant and that TS could handle parts directly, or that some parts are just not needed anymore as over time more and more ways for function declarations were added and make one another unnecessary.

Generally go over the code and see if parts can be refactored, without changing the overall functionality, I have a snapshot tests that should be able to check if the parsing is still the same (at least for examples that are committed)
Maybe as a precaution, add more examples of different things that should work to check later on (even for other issues) if these still work as expected.