Remove duplicate markup and actions from bp-legacy groups plugins template

The removed actions and markup are remnants of the original cut-and-paste
from bp-default (where plugins.php was a top-level template) into bp-legacy
(where it is not).

Fixes #5166

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7377 cdf35c40-ae34-48e0-9cc9-0c9da1808c22