Do not depend on Shadow plugin in subprojects

Since buildSrc depends on the Shadow plugin, it's already in the
classpath of all build scripts

prepare/idea-plugin/build.gradle.kts

@@ -1,19 +1,8 @@
-
 import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar
 import org.gradle.jvm.tasks.Jar
 
 description = "Kotlin IDEA plugin"
 
-buildscript {
-    repositories {
-        jcenter()
-    }
-
-    dependencies {
-        classpath("com.github.jengelman.gradle.plugins:shadow:${property("versions.shadow")}")
-    }
-}
-
 plugins {
     `java-base`
 }