Remove redundant react GridField components

[emteknetnz]

Follow on from #1857 (comment)

GridField.js and probably also GridField*.js files such as GridFieldHeader, GridFieldRow and GridFieldAction, were probably only used by campaign admin

Now that campaign admin has been removed, these components are probably redundant and can be removed

The actual regular gridfield does not have a react component

Acceptance criteria

• Remove redundant GridField react components if not used elsewhere
• If they are used elsewhere, remove references to campaigns from the component code