cmGeneratorExpressionNode: Remove dead code from ConfigurationTestNode

Commit 910ada1a88 (Genex: $<CONFIG:> syntax of all entries checked,
2023-01-17) tweaked how ConfigurationTestNode::Evaluate validates its
arguments, which resulted in the removal of the body of an `if` but not
the `if` itself. Since the condition does not have side effects, this
resulted in superfluous leftover code. Remove this.

Source/cmGeneratorExpressionNode.cxx

@@ -2227,8 +2227,6 @@ static const struct ConfigurationTestNode : public cmGeneratorExpressionNode
       return configurationNode.Evaluate(parameters, context, content, nullptr);
     }
     static cmsys::RegularExpression configValidator("^[A-Za-z0-9_]*$");
-    if (!configValidator.find(parameters.front())) {
-    }
 
     context->HadContextSensitiveCondition = true;
     bool firstParam = true;