Remove testing Kotlin signature from WriteSignatureTest

compiler/testData/writeSignature/constructor/Constructor0.kt

@@ -3,4 +3,3 @@ class Constructor0()
 // method: Constructor0::<init>
 // jvm signature:     ()V
 // generic signature: null
-// kotlin signature:  null

compiler/testData/writeSignature/constructor/ConstructorCollectionParameter.kt

@@ -4,4 +4,3 @@ class TestingKotlinCollections(val arguments: Collection<String>)
 // method: TestingKotlinCollections::<init>
 // jvm signature:     (Ljava/util/Collection;)V
 // generic signature: (Ljava/util/Collection<+Ljava/lang/String;>;)V
-// kotlin signature:  (Ljet/Collection<Ljava/lang/String;>;)null

compiler/testData/writeSignature/constructor/ConstructorWithTypeParameter.kt

@@ -3,4 +3,3 @@ class ConstructorWithTypeParameter<P>()
 // method: ConstructorWithTypeParameter::<init>
 // jvm signature:     ()V
 // generic signature: null
-// kotlin signature:  null

compiler/testData/writeSignature/constructor/ConstructorWithTypeParameterAndValueParameterP.kt

@@ -3,4 +3,3 @@ class ConstructorWithTypeParameter<P>(p: P)
 // method: ConstructorWithTypeParameter::<init>
 // jvm signature:     (Ljava/lang/Object;)V
 // generic signature: (TP;)V
-// kotlin signature:  (TP;)null