[gimp] app: remove gimp_filter_is_active() prototype

[N/A <ell src gnome org>]

commit 93ed1048c62bacbe8294958500b5cfd87f52c7ef
Author: Ell <ell_se yahoo com>
Date:   Wed Dec 6 07:23:13 2017 -0500

    app: remove gimp_filter_is_active() prototype
    
    Leftover from commit f5d1686a219fd8122a029a4783dd3da9d3627041, not
    actually defined.

 app/core/gimpfilter.h |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)
---
diff --git a/app/core/gimpfilter.h b/app/core/gimpfilter.h
index 0ac42fa..6cdd3da 100644
--- a/app/core/gimpfilter.h
+++ b/app/core/gimpfilter.h
@@ -60,7 +60,6 @@ GeglNode       * gimp_filter_peek_node        (GimpFilter     *filter);
 void             gimp_filter_set_active       (GimpFilter     *filter,
                                                gboolean        active);
 gboolean         gimp_filter_get_active       (GimpFilter     *filter);
-gboolean         gimp_filter_is_active        (GimpFilter     *filter);
 
 void             gimp_filter_set_is_last_node (GimpFilter     *filter,
                                                gboolean        is_last_node);