remove duplicate checks in interfaces.inc

(cherry picked from commit 5ad7adc6)

src/etc/inc/interfaces.inc

@@ -2990,10 +2990,6 @@ function interface_track6_6rd_configure($interface = 'lan', $lancfg)
 {
     global $config;
 
-    if (!is_array($lancfg)) {
-        return;
-    }
-
     /* If the interface is not configured via another, exit */
     if (empty($lancfg['track6-interface'])) {
         return;
@@ -3051,10 +3047,6 @@ function interface_track6_6to4_configure($interface = 'lan', $lancfg)
 {
     global $config;
 
-    if (!is_array($lancfg)) {
-        return;
-    }
-
     /* If the interface is not configured via another, exit */
     if (empty($lancfg['track6-interface'])) {
         return;