Cleanup invalid variable examples from doc

[medikoo]

As reported here #8279 (comment) we have some invalid variable examples in doc as ${self:} and ${env:}.

I've learned they're not invalid still they're controversial, and use case feels dubious. I would definitely not market them, simply to not confuse. So let's remove them from documentation.

[dsuarezlogans]

Hello good day, can I help with this issue?

[medikoo]

@dsuarezlogans Hello, certainly, that'll be very welcome!

[dsuarezlogans]

@medikoo for me to be clear on what is required, I need to remove the ${self:} and ${env:} parts of the variables in documentation for each provider right? like in here

[medikoo]

I've learned today,that this notation is actually valid, still it's controversial, and I would still not use it in examples.

So yes, it's about removing it from docs, but it should not be removed if it's the place where this specific notation is documented (I think we don't have such place, but I write this just in case)

[sleepwithcoffee]

Hi @medikoo just want to check if this is still open and valid? I might be able to help

[medikoo]

@duytrandev Yes I believe it's valid. PR's welcome!