appveyor.yml: Remove LLVM artifacts
appveyor.yml: Remove LLVM artifacts

This removes C:\\LLVM\bin from PATH and LLVM_VERSION from matrix of
appveyor.yml since 4febc53 removed libclang-py3 from the requirements.

Closes https://github.com/coala/coala/issues/5207

Nosferatul/coala,jayvdb/coala,SanketDG/coala,karansingh1559/coala,coala/coala,karansingh1559/coala,Nosferatul/coala,coala/coala,karansingh1559/coala,Nosferatul/coala,SanketDG/coala,coala-analyzer/coala,coala-analyzer/coala,jayvdb/coala,coala/coala,jayvdb/coala,SanketDG/coala,coala-analyzer/coala