GPencil: Fix missing change material menu using U key

The menu was not activated when vertex mode was enabled.

release/scripts/startup/bl_ui/properties_grease_pencil_common.py

@@ -328,11 +328,6 @@ class GPENCIL_MT_material_active(Menu):
     @classmethod
     def poll(cls, context):
         ob = context.active_object
-        tool_settings = context.scene.tool_settings
-        mode = tool_settings.gpencil_paint.color_mode
-        if mode != 'MATERIAL':
-            return False
-
         if ob is None or len(ob.material_slots) == 0:
             return False