luci-app-statistics: Remove erroneous include from default config

Remove the unnecessary Include line from the default config.
It causes error at collectd start, as the directory is missing.
  daemon.err collectd[9722]: configfile: stat (/etc/collectd/conf.d) failed: No such file or directory

Leave the line as a comment/example.

Fixes #5373

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>