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
87d7bcf274