Remove all dependencies for JCenter as it is being discontinued

[pedroduca]

Description of the issue:
https://github.com/GoogleContainerTools/jib/search?q=jcenter

JCenter is being removed, and all plugins and dependencies that have it listed as a dependency will fail fetching when they schedule their brown outs and eventually their blackouts

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

What happens after the sunset of Bintray and JCenter?

On May 1, 2021, the sunset will impact all existing Bintray users. Bintray users will be blocked and will no longer be able to use the Bintray service. This includes existing software distribution, account administrative access, UI access, and the REST API.

After this date JCenter repository will still resolve artifacts, but end users should migrate to the canonical repo (e.g. Java packages should be retrieved from Maven Central). On Feb 1st, 2022 JCenter will only resolve artifacts for Artifactory clients.

Gradle migration guide: https://blog.gradle.org/jcenter-shutdown

Expected behavior:

Dependency of jcenter is removed to avoid brown outs and a complete shutdown is planned for February 2022

Steps to reproduce:

Read articles and attempt to build a project that has Jib Gradle as a dependency during brown-out periods.

[pedroduca]

I've created the PR for this issue
#294