Remove travis, appveyor, and homebrew references in release process
Remove travis, appveyor, and homebrew references in release process

These tools have been replaced with CirrusCI,
Cloudsmith, and GitHub Actions. This removes
them from the release process documentation.

Signed-off-by: hasheddan <fff88e83cd964a817f9e74a48f8df9cd0b6b9759@gmail.com>

sgebbie/ponyc,sgebbie/ponyc,dipinhora/ponyc,ponylang/ponyc,ponylang/ponyc,dipinhora/ponyc,sgebbie/ponyc,jemc/ponyc,jemc/ponyc,ponylang/ponyc,dipinhora/ponyc,sgebbie/ponyc,jemc/ponyc,sgebbie/ponyc