Use the meson summary instead of manually building our summary with message

Testing Done:
Ran `ninja reconfigure` and verified the output.

```
purple-plugin-pack 2.8.1dev

libpurple
install directory: /usr/local/lib/purple-2
data directory : /usr/local/share
plugins : autoreply, bash, capsnot, colorize, dewysiwygification, dice, eight_ball, flip,
google, groupmsg, highlight, ignore, irc-more, irchelper, listhandler, ning,
oldlogger, omegle, showoffline, simfix, slashexec, snpp, splitter, sslinfo,
translate, xmppprio

pidgin
install directory: /usr/local/lib/pidgin
data directory : /usr/local/share
plugins : album, blistops, convbadger, difftopic, enhancedhist, gRIM, icon-override, irssi,
lastseen, listlog, mystatusbox, nicksaid, plonkers, schedule, sepandtab,
switchspell, timelog

finch
install directory: /usr/local/lib
data directory : /usr/local/share
plugins :

User defined options
backend : ninja
```

Reviewed at https://reviews.imfreedom.org/r/2408/