[BUGS-5663] Remove binding string from env config

[pwtyler]

Closes https://getpantheon.atlassian.net/browse/BUGS-5663

Summary

Reading Pantheon Environment Configuration Removes outdated reference to the binding string in various elements of the $_SERVER example. The binding ID no longer appears in these paths.

Release:

• [x] When ready
• [ ] After date: $DATE

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Post Launch

Do not remove - To be completed by the docs team upon merge:

• [ ] Redirect /old-path/ => /new-path/ (if applicable)
• [ ] Include/exclude pages ^ respectively within docs search service provider (if applicable)
• [ ] For Heroes - add a props post to the discussion board.
• [ ] Remove from the project board