Summary:
This removes Bintray/JCenter specific code and replaces it with a new plugin recommended by [Chris Banes](https://chris.banes.dev/publishing-to-maven-central/).
Pull Request resolved: https://github.com/facebook/flipper/pull/1914
Test Plan:
Manually uploaded as snapshot and full release, but with this setup still requires all sorts of manual setup, including GPG. Next PR will include automation for this.
CI here should also verify that I didn't split this diff up incorrectly.
Reviewed By: jknoxville
Differential Revision: D26367350
Pulled By: passy
fbshipit-source-id: faa6b488d6c95bc643d2f9328362e29fb4b05ded
