Move plugin-related "Suggests" from "munin-node" to plugin packages

Previously most entries in "Suggests" of "munin-node" referred to
packages that should belong to munin-plugins-core or
munin-plugins-extra instead.

The following packages were already mentioned in the relevant packages,
thus their entries are dropped instead of moved:
* libtext-csv-xs-perl
* ruby

Most other suggestions belong to munin-plugins-core.

Closes: #755257