Schema tidy-up tasks

[duncandewhurst]

These changes should already be mostly done, but in order to ensure that nothing was missed, once all the schema changes are merged into dev, we should:

• [ ] Replace any remaining common_ codelist definitions in $defs with CSV codelists and context-specific field titles and descriptions
• [ ] Remove any unreferenced definitions from $defs
• [ ] Consider whether any definitions in $defs should be in-lined (definitions that are referenced only once, do not appear in arrays array, and are not expected to be reused)
• [ ] Consider reordering the definitions in $defs in-line with their use (e.g. grouping by hazard, exposure, vulnerability and loss, higher-level before lower-level subschemas)
• [ ] Add validation keywords by running OCDS Kit's schema-strict
• [ ] Validate codelist enums (https://github.com/GFDRR/rdl-standard/pull/127)
• [ ] Check that all fields have titles and descriptions (https://github.com/GFDRR/rdl-standard/pull/128)

[duncandewhurst]

Moving straight to agreed and ready as we should be adding these keywords as we go anyway. Happy to discuss if needed, though.

[duncandewhurst]

Rather than creating many individual issues, I've updated the issue title and description to cover all the schema tidy-up tasks we'll need to do.