Remove not needed checks and code for VS2015 [VS2013 -> VS2015]

Some pragma warnings are not more needed for VS2015 compilation this
removes them.
Removing some specific code for older version than VS2015.
Forcing build to fail if compiling with VS older than VS2015.

Differential Revision: https://code.wildfiregames.com/D1396
Reviewed by: @Itms
This was SVN commit r23416.

source/third_party/cppformat/format.cpp

@@ -91,9 +91,7 @@ inline int isinfinity(long double x) { return std::isinf(x); }
 
 # pragma warning(push)
 # pragma warning(disable: 4127) // conditional expression is constant
-#if _MSC_VER > 1800
 # pragma warning(disable:4456) // hides previous local declaration
-#endif
 
 inline int getsign(double value) {
   if (value < 0) return 1;