Merge boxWithStdlib testData into box, delete BoxWithStdlib test

compiler/testData/codegen/box/jvmName/clashingErasure.kt

@@ -0,0 +1,16 @@
+// WITH_RUNTIME
+
+fun <T> List<T>.foo() = "foo"
+
+@JvmName("fooInt")
+fun List<Int>.foo() = "fooInt"
+
+fun box(): String {
+    val strings = listOf("", "").foo()
+    if (strings != "foo") return "Fail: $strings"
+
+    val ints = listOf(1, 2).foo()
+    if (ints != "fooInt") return "Fail: $ints"
+
+    return "OK"
+}