Allow secondary constructors without body

#KT-6967 Fixed

compiler/testData/diagnostics/tests/secondaryConstructors/dataClasses.kt

@@ -1,12 +1,12 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 data class A1(val x: String) {
-    constructor(): this("") {}
+    constructor(): this("")
 }
 
 data class A2() {
-    constructor(x: String): this() {}
+    constructor(x: String): this()
 }
 
 data class <!PRIMARY_CONSTRUCTOR_REQUIRED_FOR_DATA_CLASS!>A3<!> {
-    constructor() {}
+    constructor()
 }