[gthumb] removed GthSourceTree

[Paolo Bacchilega <paobac src gnome org>]

commit fe3b4601c763e29a5913a458b1f90d6e92f9e9a2
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Sat Nov 2 11:38:16 2019 +0100

    removed GthSourceTree
    
    It's not used anymore.

 gthumb/gth-source-tree.c | 386 -----------------------------------------------
 gthumb/gth-source-tree.h |  60 --------
 gthumb/meson.build       |   2 -
 3 files changed, 448 deletions(-)
---
diff --git a/gthumb/meson.build b/gthumb/meson.build
index a14db474..514d87f1 100644
--- a/gthumb/meson.build
+++ b/gthumb/meson.build
@@ -83,7 +83,6 @@ public_header_files = [
   'gth-sidebar.h',
   'gth-sidebar-section.h',
   'gth-statusbar.h',
-  'gth-source-tree.h',
   'gth-string-list.h',
   'gth-tags-entry.h',
   'gth-tags-file.h',
@@ -247,7 +246,6 @@ source_files = files(
   'gth-screensaver.c',
   'gth-sidebar.c',
   'gth-sidebar-section.c',
-  'gth-source-tree.c',
   'gth-statusbar.c',
   'gth-string-list.c',
   'gth-tags-entry.c',