[gtk/tests-cleanup] tests: Drop testbox

[Matthias Clasen <matthiasc src gnome org>]

commit b0fcf645449cc5a30b828618a465da35d7d29842
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed May 13 15:57:03 2020 -0400

    tests: Drop testbox
    
    Not useful enough to keep.
    
    See #2738

 tests/meson.build |   1 -
 tests/testbox.c   | 139 ------------------------------------------------------
 2 files changed, 140 deletions(-)
---
diff --git a/tests/meson.build b/tests/meson.build
index 356540184a..f24d147fc5 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -17,7 +17,6 @@ gtk_tests = [
   ['testappchooserbutton'],
   ['testassistant'],
   ['testbaseline'],
-  ['testbox'],
   ['testbuttons'],
   ['testcalendar'],
   ['testclipboard2'],