lib: de-conflict `log-filter` CLI command

lib: de-conflict `log-filter` CLI command

`log-filter WORD` was giving me a serious headache since it also matches
`log WORD` due to the way the CLI token handling works.  This meant that
a mistyped `log something` command would silently be interpreted as a
filter string, causing me serious headscratching and WTFs until I
figured what was going on.

Remove this UX pitfall so noone else falls into it.  (Since the command
was never saved to config, renaming it shouldn't cause trouble.)

[Also I apparently forgot to update the docs when I transferred this
over to the new zlog bits...]

TODO for a rainy day:  since we collect all the CLI commands anyway, we
should warn somewhere for "2nd level ambiguous" commands like this.

Signed-off-by: David Lamparter <equinox@diac24.net>