Remove jcenter from list of repositories

[gastaldi]

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

[slonopotamus]

Note that this is not the only dependency on jcenter/bintray in testcontainers.

As far as I understand, testcontainers currently publishes its releases via bintray: https://github.com/testcontainers/testcontainers-java/blob/master/gradle/bintray.gradle

[bsideup]

@gastaldi could you please remove it from everywhere, not only the top level file? There are a few entries (e.g. examples)

[gastaldi]

@bsideup My Gradle-fu is a bit limited, but I think I removed every reference from the repository, except for the RELEASING.md, which says that Bintray syncs with Central and I have no idea how to do that in Gradle :)

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If you believe this is a mistake, please reply to this comment to keep it open. If there isn't one already, a PR to fix or at least reproduce the problem in a test case will always help us get back on track to tackle this.

[rnorth]

It's not quite as easy as this; we need to replace our bintray publication with something else, and I'm afraid that this is a task that core maintainers need to do.

Removal of jcenter() from repositories blocks is still valuable, though!

[bsideup]

Seems to be superseeded by #4931, sorry! Thanks for your time working on this PR tho, much appreciated!