Replace various compression_gain functions

[magnetophon]

Similar to #86, there's some code of mine that recently was added to the libraries so when the faust version is updated we can switch to the upstream versions.

Code in master_me is here and here.

[trummerschlunk]

Are the upstream versions being used already?
Meaning, I can just delete these parts?

Edit: ah, still waiting for homebrew, I guess...

[magnetophon]

The latest faust release doesn't even have the code yet.
Most pkg managers, including homebrew, only package the release versions.

[sletz]

Next Faust release hopefully at the end of september

[magnetophon]

There's been a release, so we could do this.
Do we want to?
Let me know, I'll make the change.

[trummerschlunk]

Could it cause any trouble on @falkTX 's side? If not, please go ahead - thank you !