Build: don't reset `healthcheck` when updating builds (#12493)
At different points during the build process (including before finishing
it), we update the `Build` object via the API with new values (e.g.
state, length, etc) re-using the `APIBuild` object we fetched via the
API before starting the build.
Since that object contains `APIBuild.healthcheck` _we are resetting_ the
healthcheck before finishing the build.
This commit removes the `healthcheck` field from the `APIBuild`
returned, so it's not updated by the build while it's being executed.