Revert "Add native_testing library to mock @Native classes"

tests/compiler/dart2js_native/dart2js_native.status

Index: tests/compiler/dart2js_native/dart2js_native.status
diff --git a/tests/compiler/dart2js_native/dart2js_native.status b/tests/compiler/dart2js_native/dart2js_native.status
index 874ace3634b17df3a2c81beed4afa84465088149..080c6e1dde34b1be6123d3f5031df1712fce062c 100644
--- a/tests/compiler/dart2js_native/dart2js_native.status
+++ b/tests/compiler/dart2js_native/dart2js_native.status
@@ -25,3 +25,11 @@ optimization_hints_test: Fail, OK # Test relies on unminified names.
 
 [ $compiler == dart2js && $runtime == d8 && $system == windows ]
 compute_this_script_test: Skip # Issue 17458
+
+[ $compiler == dart2js && $cps_ir ]
+foreign_test: RuntimeError # Expect.equals(expected: <1234567891011>, actual: <1234567891011>) fails.
+native_exception_test: RuntimeError # Issue 24421
+optimization_hints_test: RuntimeError # Please triage this failure.
+
+[ $compiler == dart2js && $cps_ir && $checked ]
+*: Skip # `assert` not implemented, 75% of the tests fail.