[glibmm] Remove obsolete comment.

[Murray Cumming <murrayc src gnome org>]

commit dbb1c852443509edd7b5bfca3ace8265859bc5b6
Author: Murray Cumming <murrayc murrayc com>
Date:   Tue Sep 17 09:58:17 2013 +0200

    Remove obsolete comment.

 glib/src/variant.hg |    3 ---
 1 files changed, 0 insertions(+), 3 deletions(-)
---
diff --git a/glib/src/variant.hg b/glib/src/variant.hg
index e7b6066..1f905fc 100644
--- a/glib/src/variant.hg
+++ b/glib/src/variant.hg
@@ -68,9 +68,6 @@ namespace Glib
  */
 _WRAP_GERROR(VariantParseError, GVariantParseError, G_VARIANT_PARSE_ERROR, NO_GTYPE)
 
-//TODO: VariantBase class can be copied, so suggest how it can be dynamic casted to
-//derived types: See https://bugzilla.gnome.org/show_bug.cgi?id=644146
-
 //TODO: Add this documentation from the API if we are confident of it for the C++ wrapper:
 // #GVariant is completely threadsafe.  A #GVariant instance can be
 // concurrently accessed in any way from any number of threads without