QRandom: drop a usage of std::is_literal_type

It's deprecated/removed, and indeed doesn't check anything that it's
not also already being checked by the previous line.

Change-Id: Ic80ca43f390dd989ced69f196efa7313069e7c6d
Pick-to: 5.15 6.0 6.1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/global/qrandom.cpp

@@ -377,7 +377,6 @@ struct QRandomGenerator::SystemAndGlobalGenerators
 
         constexpr SystemAndGlobalGenerators g = {};
         Q_UNUSED(g);
-        static_assert(std::is_literal_type<SystemAndGlobalGenerators>::value);
 #endif
     }