[gimp] vala: Fix some metadata warnings

[Niels De Graef <nielsdg src gnome org>]

commit 23d5ef25467572c3a3aab53aca71c6bfe807f680
Author: Niels De Graef <nielsdegraef gmail com>
Date:   Tue May 26 22:04:01 2020 +0200

    vala: Fix some metadata warnings
    
    We were mentioning some symbols that aren't introspected, because they
    are part of `app/*`.

 libgimp/GimpUi-3.0.metadata | 10 ----------
 1 file changed, 10 deletions(-)
---
diff --git a/libgimp/GimpUi-3.0.metadata b/libgimp/GimpUi-3.0.metadata
index 6397503fd1..4353d26be7 100644
--- a/libgimp/GimpUi-3.0.metadata
+++ b/libgimp/GimpUi-3.0.metadata
@@ -11,15 +11,5 @@ IntComboBox
   .new skip=false
 IntStore
   .new skip=false
-MessageDialog
-  .new skip=false
 ProcBrowserDialog
   .new skip=false
-ToolDialog
-  .new skip=false
-OverlayDialog
-  .new skip=false
-ViewableDialog
-  .new skip=false
-
-text_layer_set