When Travis updates the homebrew cache in their images, stop updating it in .travis.yml

In legacy/trac#30928 (moved), we added a homebrew update to .travis.yml for shellcheck. legacy/trac#30279 (moved) also uses an updated tor for the IPv6 v3 single onion service job.

This ticket removes that update.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information