dev/ci: remove set -x in all tests

Created by: bobheadxi

IMO the utility of these are quite debatable, and they make CI output quite difficult to read. Things we can do instead:

• Just add set -x when you're debugging something
• Add better messages with echo
• Move things to sg where we might be able to add a -debug mode one day

Test plan

main-dry-run: https://buildkite.com/sourcegraph/sourcegraph/builds/152078