Fix CI

[chnn]

Closes #4055

• Empty cache before building ui on CircleCI
• Remove unused targets from Makefile

[chnn]

Tests are failing due to Yarn registry downtime at the moment. You can never win 😝

[jaredscheib]

Looks good to me. While we're here, would you mind fixing the fact that from time to time, both for me and for multiple other devs lately, make will fail after a make clean due to ui/build not existing? I believe changing line 88 to cd ui && mkdir build && yarn --no-progress --no-emoji would solve this.

[jaredscheib]

My guess btw is that something like parcel-bundler/parcel#637 is what's causing CircleCI to fail. I've seen Parcel get stuck on different files during build, and never get over that hurdle. So presumably this is triggering Circle's 10m timeout rule. I've noticed that using make clean gets Parcel back into working order, so presumably yarn run clean will do the same thing, as implemented in this PR.