Drop kotin/kotlinx and kotlin/kotlinx.html bintray usages (KTI-528)

plugins/imports-dumper/build.gradle.kts

@@ -6,10 +6,6 @@ plugins {
     id("jps-compatible")
 }
 
-repositories {
-    maven("https://dl.bintray.com/kotlin/kotlinx")
-}
-
 val kotlinxSerializationVersion = "0.4.2"
 
 dependencies {

plugins/kotlin-serialization/kotlin-serialization-compiler/README.md

@@ -3,8 +3,6 @@
 Kotlin serialization plugin consists of three parts: a compiler plugin, an IntelliJ plugin and a runtime library.
 This is the folder with common source for all plugins, IDEA plugin is built from here. Gradle and Maven plugins can be found in `libraries` folder.
 
-Compiler plugins are uploaded on bintray: https://bintray.com/kotlin/kotlinx/kotlinx.serialization.plugin
-
 ## Building and usage
 
 ### Prerequisites: