update payloads for msg spec 5

- remove auto_rewrite_input
- remove doctest_mode
- remove exit key from ask_exit
- rename 'edit_magic' to 'edit'
- remove screen_lines from page

remaining payloads ('edit', 'ask_exit', 'set_next_input', 'page')
are documented as deprecated in the msg spec
Merge pull request #7005 from minrk/payloads-3.0

update payloads for msg spec 5