Remove circleci folder (facebook#49121)

Summary:
Pull Request resolved: facebook#49121

This change removes the scripts/circleci folder and the last poll-maven script which was not used.

## Changelog:
[Internal] - Remove the circleci folder script

Reviewed By: cortinico, huntie

Differential Revision: D69047603

fbshipit-source-id: a4f1f100d71d792edf42c8d4cb6a0b8d8e7e5260