Use shorthand factories for maven repositories

Remove unused repository for kotlinx-metadata-jvm which now comes from Maven Central.

Change-Id: I273e1c69a4466e840e40cf6efd249ed0ffed8f6d
diff --git a/build.gradle b/build.gradle
index 07b22f9..a3a14fb 100644
--- a/build.gradle
+++ b/build.gradle
@@ -18,9 +18,7 @@
             url 'http://storage.googleapis.com/r8-deps/maven_mirror/'
         }
         mavenCentral()
-        maven {
-            url "https://plugins.gradle.org/m2/"
-        }
+        gradlePluginPortal()
         jcenter()
     }
     dependencies {
@@ -58,9 +56,8 @@
     maven {
        url 'http://storage.googleapis.com/r8-deps/maven_mirror/'
     }
-    maven { url 'https://maven.google.com' }
+    google()
     mavenCentral()
-    maven { url 'https://kotlin.bintray.com/kotlinx' }
 }
 
 if (project.hasProperty('with_code_coverage')) {