Update built dependency to 0.7.1 (#452)

* Update built dependency to 0.7.1

Requires some small changes to the code, as the Option struct has been removed in favor of feature flags.

* Switch to a patched fork of the built crate to avoid writing out the environment, because this breaks in our Tilt workflow.

* Renamed branch on fork to include version.

* Added comment on why we need this override.

* Switched to the PR branc which introduces a feature gate for this line.

* Moved comment line, as it only applies to the one specific patch, not the entire crates.io patch section.