New policy to remove roles

[pllim]

As brought up by @dhomeier in #460 (comment)

[dhomeier]

In principle this applies to both removing people from roles, and roles themselves (which I primarily had in mind).
I think so far this has just been done more informally by CoCo when the case for the role was no longer given; most recent precedents would be astropy/astropy.github.com#613 and astropy/astropy.github.com#634.

[pllim]

Would ease my pain for this issue, for sure...

• Roles: Audit all existing titles and membership astropy.github.com#519

p.s. #430 (comment)