Revert "avoid warnings about deprecated decls. from glib2"

This reverts commit a206bc22.  While removing
the GLIB_DISABLE_DEPRECATION_WARNINGS defines does not lead to problems at least
with my current Fedora 18 environment (and, according to dtardon, "guessing by
the date, it was on f16 or f17" where that fix was relevant), having the defines
does cause -Werror=unused-macros at least in one RHEL 6 environment.

So I'm reverting for now, in the hope that should any warnings re-appear, they
can be addressed by applying the recent s/-I/$IFLAGS/ approach to GTK_CFLAGS in
configure.ac.

Change-Id: I5a3e4efabb88eb06304dd8b9eee6d8867fd77be5

vcl/unx/gtk/app/gtkdata.cxx

@@ -30,7 +30,6 @@
 #include <sys/types.h>
 #include <sys/time.h>
 #endif
-#define GLIB_DISABLE_DEPRECATION_WARNINGS
 #include <unx/gtk/gtkdata.hxx>
 #include <unx/gtk/gtkinst.hxx>
 #include <unx/gtk/gtkframe.hxx>

vcl/unx/gtk/app/gtkinst.cxx

@@ -21,7 +21,6 @@
 #include <stack>
 #include <string.h>
 #include <osl/module.h>
-#define GLIB_DISABLE_DEPRECATION_WARNINGS
 #include <unx/gtk/gtkdata.hxx>
 #include <unx/gtk/gtkinst.hxx>
 #include <unx/salobj.h>