Delete generated test cases, move testData to boxWithStdlib

compiler/testData/codegen/boxWithStdlib/dataClasses/tostring/genericParam.kt

@@ -0,0 +1,11 @@
+data class A<T>(val x: T)
+
+fun box(): String {
+    val a = A(42)
+    if ("$a" != "A(x=42)") return "$a"
+    
+    val b = A(239.toLong())
+    if ("$b" != "A(x=239)") return "$b"
+    
+    return "OK"
+}