Don't reseed std::srand when resetting rng state

We no longer use `std::rand` anywhere, so there is no point,
and it might even interfere with our users use of `std::(s)rand`.

src/catch2/internal/catch_run_context.cpp

@@ -599,7 +599,6 @@ namespace Catch {
 
     void seedRng(IConfig const& config) {
         if (config.rngSeed() != 0) {
-            std::srand(config.rngSeed());
             rng().seed(config.rngSeed());
         }
     }