[gnome-software] trivial: Remove an unused function prototype

[Kalev Lember <klember src gnome org>]

commit 6ff8bc86f3b43cc1c16054cbc6f3dda42c3e0e37
Author: Kalev Lember <kalevlember gmail com>
Date:   Sat May 30 00:08:37 2015 +0200

    trivial: Remove an unused function prototype
    
    Leftover from commit 46eca30b6786b66af9c8eeac1f64f1ffdd6fbc0b that
    removed online update functionality.

 src/gs-plugin.h |    4 ----
 1 files changed, 0 insertions(+), 4 deletions(-)
---
diff --git a/src/gs-plugin.h b/src/gs-plugin.h
index 0269619..ccc2977 100644
--- a/src/gs-plugin.h
+++ b/src/gs-plugin.h
@@ -229,10 +229,6 @@ gboolean    gs_plugin_app_install                  (GsPlugin       *plugin,
                                                         GsApp          *app,
                                                         GCancellable   *cancellable,
                                                         GError         **error);
-gboolean        gs_plugin_app_update                   (GsPlugin       *plugin,
-                                                        GsApp          *app,
-                                                        GCancellable   *cancellable,
-                                                        GError         **error);
 gboolean        gs_plugin_app_remove                   (GsPlugin       *plugin,
                                                         GsApp          *app,
                                                         GCancellable   *cancellable,