temporarily disable opengl in test_runtime_ndarray.py (#804)

tests/python/unittest/test_runtime_ndarray.py

@@ -7,8 +7,7 @@ def enabled_ctx_list():
                 ('cl', tvm.opencl(0)),
                 ('metal', tvm.metal(0)),
                 ('rocm', tvm.rocm(0)),
-                ('vpi', tvm.vpi(0)),
-                ('opengl', tvm.opengl(0))]
+                ('vpi', tvm.vpi(0))]
     for k, v  in ctx_list:
         assert tvm.context(k, 0) == v
     ctx_list = [x[1] for x in ctx_list if x[1].exist]