Remove useless stuff in third_party folders

[jmarrec]

Issue overview

third_party folders are purposely not git submodules, so they should carry the source code, not all the things around it such as .github subfolders, etc. btwxt is definitely an offender, I don't know if there are any others.

Prompted by my git client constantly complaining (everytime I switch branches) that the courrier vendor googletest has no url: https://github.com/NREL/EnergyPlus/tree/develop/third_party/btwxt/vendor/courierr/vendor

Details

Some additional details for this issue (if relevant):

• Platform (Operating system, version)
• Version of EnergyPlus (if using an intermediate build, include SHA)

AFAIK, this was introduced in #10160

https://github.com/NREL/EnergyPlus/pull/10160/files#diff-9b605f18678db20624e8f2e9c98685f229f09906845df78a9f27a4ef861b9203

Checklist

Add to this list or remove from it as applicable. This is a simple templated set of guidelines.

• Defect file added (list location of defect file here)
• Ticket added to Pivotal for defect (development team task)
• Pull request created (the pull request will have additional tasks related to reviewing changes that fix this defect)

[nealkruis]

I'll look into this. Most of these files can be removed as long as they are also ignored so they don't cause trouble for people developing them from their native repositories.

[jmarrec]

FYI I'm still hitting this on the daily.