[churn] Drop Perforce support from codebase (allow to compile without Perforce connection)

[dimhotepus]

• SImplifies code base.
• Small teams usually do not use Perforce.

[dimhotepus]

Partially done in https://github.com/Source-Authors/Obsoletium/commit/4189292895c9ce6dde9dfbd8be6f9542705ef96a

At least now can build without Perforce.