Move test.kt stubs to smallRuntime

We already use kotlin.test with fullRuntime klib.

libraries/stdlib/js-ir/smallRuntime/tests.kt

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.test
+
+// This file plugs some declaration from "kotlin.test" library used in tests.
+
+fun <T> assertEquals(a: T, b: T) {
+    if (a != b) throw Exception("")
+}
+
+fun assertTrue(x: Boolean) {
+    if (!x) throw Exception("")
+}
+
+fun assertFalse(x: Boolean) {
+    if (x) throw Exception("")
+}
+
+fun <T : Any> assertNotNull(actual: T?, message: String? = null): T {
+    if (actual == null) throw Exception("")
+    return actual
+}
+
+