Drop type aliases for JS and KLIB string tables

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

compiler/util-klib-metadata/src/org/jetbrains/kotlin/library/metadata/KlibMetadataStringTable.kt

@@ -1,10 +0,0 @@
-/*
- * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
- */
-
-package org.jetbrains.kotlin.backend.common.serialization.metadata
-
-import org.jetbrains.kotlin.serialization.ApproximatingStringTable
-
-typealias KlibMetadataStringTable = ApproximatingStringTable