Merge boxWithStdlib testData into box, delete BoxWithStdlib test

compiler/testData/codegen/box/reflection/genericSignature/covariantOverride.kt

@@ -0,0 +1,18 @@
+// WITH_REFLECT
+
+interface A {
+    fun foo(): Collection<Any>
+}
+
+abstract class B : A {
+    override fun foo(): Collection<String> = null!!
+}
+
+fun box(): String {
+    val clazz = B::class.java
+    if (clazz.declaredMethods.first().genericReturnType.toString() != "java.util.Collection<java.lang.String>") return "fail 1"
+
+    if (clazz.methods.filter { it.name == "foo" }.size != 1) return "fail 2"
+
+    return "OK"
+}