Undocument PYFLUENT_FLUENT_ROOT

[seanpearsonuk]

Users are misusing this; e.g., it does not resolve CAD reader locations without AWP variables being set (#1572). It would be simpler to leave it out - it was not intended for general usage.

@dnwillia @mkundu1 do you agree to remove or only add some caveat?
@acarvalh-work - the work is pending final decision how to proceed.

https://fluent.docs.pyansys.com/release/0.13/api/general/launcher/index.html

[mkundu1]

@seanpearsonuk @acarvalh-work I'm OK to remove the env. var. It was meant for internal developers. Please also update the FAQ: https://fluent.docs.pyansys.com/release/0.13/getting_started/faqs.html#how-does-pyfluent-infer-the-location-to-launch-fluent

[dnwillia-work]

Yes, agree that we should remove the documentation. It's meant for pointing to a local Fluent build area which the library users will almost never have.

Also needs removal from the README:

https://github.com/ansys/pyfluent#launching-fluent

[mkundu1]

@acarvalh-work @seanpearsonuk We also need to make this change in release/0.13 to update the stable documentation. Patch version won't be required, running the release-doc-build after merge should deploy the latest stable doc.