Misc mdoc fixes:

- Remove superfluous paragraph macros.
- Remove/fix empty or incorrect macros.
- Sort sections into conventional order.
- Terminate quoted strings properly.
- Remove EOL whitespace.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274925 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f