libstdcompat: removed duplicate build-time test method (#44725)

* libstdcompat: removed stand-alone test method

var/spack/repos/builtin/packages/libstdcompat/package.py

@@ -107,8 +107,3 @@ def cmake_args(self):
         else:
             args.append("-DBUILD_TESTING=OFF")
         return args
-
-    @run_after("build")
-    @on_package_attributes(run_tests=True)
-    def test(self):
-        make("test")