Build: drop IntelliJ 2018.3 support (KT-35374)

Delete references in code

idea/idea-maven/src/org/jetbrains/kotlin/idea/maven/KotlinMavenArtifactsDownloadScheduler.kt

@@ -1,21 +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.idea.maven
-
-import org.jetbrains.concurrency.AsyncPromise
-import org.jetbrains.idea.maven.model.MavenArtifact
-import org.jetbrains.idea.maven.project.MavenProject
-import org.jetbrains.idea.maven.project.MavenProjectsManager
-
-//BUNCH: 183
-fun scheduleArtifactsDownloading(
-    projectsManager: MavenProjectsManager,
-    projects: List<MavenProject>,
-    toBeDownloaded: List<MavenArtifact>
-) {
-    //true, false, AsyncResult()
-    projectsManager.scheduleArtifactsDownloading(projects, toBeDownloaded, true, false, AsyncPromise())
-}

idea/idea-maven/src/org/jetbrains/kotlin/idea/maven/KotlinMavenImporter.kt

@@ -17,6 +17,7 @@ import com.intellij.openapi.roots.libraries.Library
 import com.intellij.util.PathUtil
 import org.jdom.Element
 import org.jdom.Text
+import org.jetbrains.concurrency.AsyncPromise
 import org.jetbrains.idea.maven.importing.MavenImporter
 import org.jetbrains.idea.maven.importing.MavenRootModelAdapter
 import org.jetbrains.idea.maven.model.MavenPlugin
@@ -129,7 +130,8 @@ class KotlinMavenImporter : MavenImporter(KOTLIN_PLUGIN_GROUP_ID, KOTLIN_PLUGIN_
         val toBeDownloaded = artifacts.filter { it.libraryName in libraryNames }
 
         if (toBeDownloaded.isNotEmpty()) {
-            scheduleArtifactsDownloading(MavenProjectsManager.getInstance(module.project), listOf(mavenProject), toBeDownloaded)
+            MavenProjectsManager.getInstance(module.project)
+                .scheduleArtifactsDownloading(listOf(mavenProject), toBeDownloaded, true, false, AsyncPromise())
         }
     }