Fix streamexpect install dependency issue

[pkendall64]

This back-ports the inclusion of streamexpect into the ExpressLRS code base, therefore not requiring a pip install which cause the breakage because the setup.py for streamexpect depended on setuptools-markdown which depended on pypandoc which got upgraded in an incompatible way and all the dependencies are >=, which is "problematic".

[deadbytefpv]

Suggested this PR for quite a few users within the day and they were able to build and flash their devices.
Thanks PK!

[YQBen]

Sorry I'm new to this, I also got the erro that module 'pypandoc' has no attribute 'convert', looks like the solution is here, is the thing I should do to add the 3 .py files into the src folder and try to build again? I tried and got this
ModuleNotFoundError: No module named 'external':

em... sorry again for such a basic question.

[deadbytefpv]

Sorry I'm new to this, I also got the erro that module 'pypandoc' has no attribute 'convert', looks like the solution is here, is the thing I should do to add the 3 .py files into the src folder and try to build again? I tried and got this ModuleNotFoundError: No module named 'external':

em... sorry again for such a basic question.

You should be building 2.5.0 (or the latest 2.5.1) firmware now as the fix for this issue is already there.