Drop type aliases for JS and KLIB string tables

They used to use the same approximation logic anyway
^KT-20996

js/js.serializer/src/org/jetbrains/kotlin/serialization/js/JavaScriptStringTable.kt

@@ -1,21 +0,0 @@
-/*
- * Copyright 2010-2016 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.jetbrains.kotlin.serialization.js
-
-import org.jetbrains.kotlin.serialization.ApproximatingStringTable
-
-typealias JavaScriptStringTable = ApproximatingStringTable

js/js.serializer/src/org/jetbrains/kotlin/serialization/js/KotlinJavascriptSerializerExtension.kt

@@ -26,6 +26,7 @@ import org.jetbrains.kotlin.metadata.serialization.MutableVersionRequirementTabl
 import org.jetbrains.kotlin.psi.KtFile
 import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.source.PsiSourceFile
+import org.jetbrains.kotlin.serialization.ApproximatingStringTable
 import org.jetbrains.kotlin.serialization.DescriptorSerializer
 import org.jetbrains.kotlin.serialization.KotlinSerializerExtensionBase
 import org.jetbrains.kotlin.types.FlexibleType
@@ -35,7 +36,7 @@ class KotlinJavascriptSerializerExtension(
     private val languageVersionSettings: LanguageVersionSettings,
     override val metadataVersion: BinaryVersion
 ) : KotlinSerializerExtensionBase(JsSerializerProtocol) {
-    override val stringTable = JavaScriptStringTable()
+    override val stringTable = ApproximatingStringTable()
 
     override fun serializeFlexibleType(flexibleType: FlexibleType, lowerProto: ProtoBuf.Type.Builder, upperProto: ProtoBuf.Type.Builder) {
         lowerProto.flexibleTypeCapabilitiesId = stringTable.getStringIndex(DynamicTypeDeserializer.id)