Remove experimental.coroutines DSL

And 'kotlin.coroutines' property as well.

^KT-50494 Fixed

libraries/tools/kotlin-gradle-plugin-model/src/main/kotlin/org/jetbrains/kotlin/gradle/model/ExperimentalFeatures.kt

@@ -1,20 +0,0 @@
-/*
- * Copyright 2010-2018 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.gradle.model
-
-/**
- * Wraps all experimental features information for a given Kotlin project.
- * @see KotlinProject
- */
-interface ExperimentalFeatures {
-
-    /**
-     * Return coroutines string.
-     *
-     * @return coroutines.
-     */
-    val coroutines: String?
-}

libraries/tools/kotlin-gradle-plugin-model/src/main/kotlin/org/jetbrains/kotlin/gradle/model/KotlinProject.kt

@@ -68,11 +68,4 @@ interface KotlinProject {
      * @return expectedBy dependencies.
      */
     val expectedByDependencies: Collection<String>
-
-    /**
-     * Return an object containing a descriptor of the experimental features.
-     *
-     * @return experimental features.
-     */
-    val experimentalFeatures: ExperimentalFeatures
 }