glibcompat: remove g_direct_equal shim
This function is present at least in glib-2.43.92:
../../lib/glibcompat.c:69:1: error: static declaration of 'g_direct_equal' follows non-static declaration
69 | g_direct_equal (gconstpointer v1, gconstpointer v2)
| ^~~~~~~~~~~~~~
In file included from /home/zaytsev/opt/glib/include/glib-2.0/glib.h:50,
from ../../lib/global.h:10,
from ../../lib/glibcompat.c:36:
/home/zaytsev/opt/glib/include/glib-2.0/glib/ghash.h:180:10: note: previous declaration of 'g_direct_equal' was here
180 | gboolean g_direct_equal (gconstpointer v1,
| ^~~~~~~~~~~~~~
Signed-off-by: Yury V. Zaytsev <yury@shurup.com>