Remove link to the registration page, since the registration page actually...

Remove link to the registration page, since the registration page actually takes you to the homepage when you're logged in.
(cherry picked from commit c2609f01)

htdocs/lang/en.utf8/help/forms/institution.registerallowed.html

 <h3>Registration allowed?</h3>
-<p>If this setting is enabled, users will be able to register for the site using the <a href="../../../register.php">registration form</a>.</p>
+<p>If this setting is enabled, users will be able to register for the site using the registration form.</p>
 <p>If more than one institution has this setting enabled, the user will be able to choose which institution they wish to register for using a dropdown.</p>
 <p>If no institutions have this setting enabled, then users will not be able to register using the registration form.</p>
 <p>In general, if you have users set up to join this institution through a mechanism such as LDAP login or SSO from an external application, you should turn this setting off. You should also turn it off if you wish to control the creation of accounts using the <a href="add.php" target="_blank">Add User</a> or <a href="uploadcsv.php" target="_blank">Add Users By CSV</a> pages.</p>