+ simplify EuiForm/form to 1 level of nesting

…late props

- now that the header/actions, chrome/telemetry, & empty state etc. are all DRY'd out by the template, there's no need for a separate header component
- we can simply dry out the header action, which will shortly be removed with the 7.14 launch

- note: for empty state changes: mostly indenting, the new template automatically creates a subdued panel for us in empty state so no need to include one manually

I definitely should not have been importing the index file I'm mocking, but why did this only break now?? :psyduck: