[#53792115] Remove all traces of the `validating` status from the code.

- Fix the web responses UI so it works without `validating`
- Haven't touched mobile responses yet.
- This will probably break the build.
- (on web) incomplete response with errors > mark as complete > save as
  draft button is missing. This is because the `response` instance
variable has `status` set to `complete`, even though this isn't
persisted. Need to reload just this attribute.
[#53792115] Fix responses_spec