Make blog selection in recentposts blocktype not required.

This matches previous changes that we did so all blocks could be used in
Views regardless of whether they were copyable.
Signed-off-by: Nigel McNie <nigel@catalyst.net.nz>

htdocs/artefact/blog/blocktype/recentposts/lib.php

@@ -90,9 +90,6 @@ class PluginBlocktypeRecentposts extends PluginBlocktype {
             'type'  => 'artefactchooser',
             'title' => get_string('blogs', 'artefact.blog'),
             'defaultvalue' => $default,
-            'rules' => array(
-                'required' => true,
-            ),
             'blocktype' => 'recentposts',
             'limit'     => 10,
             'selectone' => false,