Remove redundant var from checkbox sprintf

The var $value was not used and can be removed from the call.

Signed-off-by: Roi Dayan <roi.dayan@gmail.com>

Author: roidayan

class.settings-api.php

@@ -172,7 +172,7 @@ function callback_checkbox( $args ) {
         $value = esc_attr( $this->get_option( $args['id'], $args['section'], $args['std'] ) );
 
         $html = sprintf( '<input type="hidden" name="%1$s[%2$s]" value="off" />', $args['section'], $args['id'] );
-        $html .= sprintf( '<input type="checkbox" class="checkbox" id="wpuf-%1$s[%2$s]" name="%1$s[%2$s]" value="on"%4$s />', $args['section'], $args['id'], $value, checked( $value, 'on', false ) );
+        $html .= sprintf( '<input type="checkbox" class="checkbox" id="wpuf-%1$s[%2$s]" name="%1$s[%2$s]" value="on" %3$s />', $args['section'], $args['id'], checked( $value, 'on', false ) );
         $html .= sprintf( '<label for="wpuf-%1$s[%2$s]"> %3$s</label>', $args['section'], $args['id'], $args['desc'] );
 
         echo $html;