Remove test for gcc -Wuseless-cast constructor inheritance bug

The bug is fixed in all supported versions of gcc, so there is no need
to test for it anymore.

SConstruct

@@ -2439,37 +2439,9 @@ $ x86_64-pc-linux-gnu-g++-5.4.0 -x c++ -S -Wformat -o /dev/null -
  */
 #include <SDL_endian.h>
 
-/*
- * Recent gcc[1] create a useless cast when synthesizing constructor
- * inheritance, then warn the user about the compiler-generated cast.
- * Since the user did not write the cast in the source, the user
- * cannot remove the cast to eliminate the warning.
- *
- * The only way to avoid the problem is to avoid using constructor
- * inheritance in cases where the compiler would synthesize a useless
- * cast.
- *
- * Reported-by: zicodxx <https://github.com/dxx-rebirth/dxx-rebirth/issues/316>
- * gcc Bugzilla: <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70844>
- *
- * [1] gcc-6.x, gcc-7.x (all currently released versions)
- */
-class base
-{
-public:
-	base(int &) {}
-};
-
-class derived : public base
-{
-public:
-	using base::base;
-};
-
 ''', main='''
-	derived d(argc);
 	return SDL_Swap32(argc);
-''', msg='whether compiler argument -Wuseless-cast works with SDL and with constructor inheritance', successflags=flags):
+''', msg='whether compiler argument -Wuseless-cast works with SDL', successflags=flags):
 			return
 		# <=clang-3.7 does not understand -Wuseless-cast
 		# This test does not influence the compile environment, but is