[jabley] remove `homebrew/science` tap
[jabley] remove `homebrew/science` tap

This was originally included to install `R`. I don’t need this for now.

See https://github.com/alphagov/gds-boxen/commit/051b15a02cdd55989bfad483fb6da808ab01a454

`R` is now part of `brew cask` if I do want it in the future.
jabley/our-boxen,jabley/our-boxen,jabley/our-boxen