This was older code from before we had modular features, and is no longer required as modular features already load and register themselves.
[CL 2493586 by Jamie Dale in Main branch]
TTP# 342872 - EDITOR: Regression: CRASH: FSourceControlModule::ShutdownModule
The SVN source control provider module was being shutdown before the main source control module, leading to a crash.
The source control module now watches for its active provider module being unloaded, and will gracefully reset itself to the default (dummy) provider if that happens.
I also added these same checks to the source code access module, as it uses the same provider modules mechanism.
#codereview Thomas.Sarkanen, Max.Preussner
[CL 2244286 by Jamie Dale in Main branch]
