build.gradle: remove all remaining references to the JCenter repository

build.gradle

@@ -5,7 +5,6 @@ buildscript {
     repositories {
         mavenCentral()
         google()
-        jcenter()
         maven {
             url "https://plugins.gradle.org/m2/"
         }
@@ -21,7 +20,6 @@ allprojects {
     repositories {
         mavenCentral()
         google()
-        jcenter()
     }
 }