KAFKA-12293: Remove JCenter from buildscript and delete buildscript.gradle

They're no longer used and JFrog is sunsetting JCenter.

https://jfrog.com/blog/into-the-sunset-bintray-jcenter-gocenter-and-chartcenter

Reviewers: Ismael Juma <ismael@juma.me.uk>

build.gradle

@@ -20,9 +20,7 @@ import java.nio.charset.StandardCharsets
 buildscript {
   repositories {
     mavenCentral()
-    jcenter()
   }
-  apply from: file('gradle/buildscript.gradle'), to: buildscript
   apply from: "$rootDir/gradle/dependencies.gradle"
 
   dependencies {
@@ -1975,7 +1973,7 @@ project(':connect:transforms') {
 
   dependencies {
     api project(':connect:api')
-    
+
     implementation libs.slf4jApi
 
     testImplementation libs.easymock

gradle/buildscript.gradle

@@ -1,23 +0,0 @@
-// Licensed to the Apache Software Foundation (ASF) under one or more
-// contributor license agreements.  See the NOTICE file distributed with
-// this work for additional information regarding copyright ownership.
-// The ASF licenses this file to You under the Apache License, Version 2.0
-// (the "License"); you may not use this file except in compliance with
-// the License.  You may obtain a copy of the License at
-//
-//    http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-repositories {
-  repositories {
-    // For license plugin.
-    maven {
-      url 'https://dl.bintray.com/content/netflixoss/external-gradle-plugins/'
-    }
-  }
-}