Fix getter/setter section contains misinformation

[mootari]

Removes the "Getter / Setter" section from the best practices guide because it violates TypeScript standards and best practices: The TypeScript guide on Do's and Don'ts explicitely states that optional parameters are to be preferred.

[mootari]

As a side note, a link to the TypeScript Do's and Don'ts should probably be featured prominently on that page, as those already cover most of the points.

[mootari]

I just realized that the section is meant to describe combined setters / getters with argument dependant return values. Sorry for the noise. (Could probably be made a bit more verbose though)