Stop checking if ruby2_keywords is defined

[casperisfine]

Now that Ruby 2.7+ is required, we can assume ruby2_keywords is available.

cc @kamipo

[rafaelfranca]

We don't call method modifiers in the same line as the method definition. I'll change it to be after the method definition like it was before.

[byroot]

Sorry, didn't know. I can clean it up if you want.

[rafaelfranca]

I already did. BTW, do we still need to call it if we are only supporting Ruby 2.7? Can't we split the args from kwargs in all those methods?

[byroot]

Unfortunately no, it's still ambiguous on 2.7. So they'll have to stay until support for it is dropped.