Re-enable raising deprecation warnings

[astrofrog]

Just disable this for visual tests due to widgetti/solara#171

[dhomeier]

I think this will need the following updates to ignores:

-    ignore:Keyword `trait:DeprecationWarning:pythreejs.*:
+    ignore:Keyword `trait` is deprecated in traitlets.*:DeprecationWarning:bqplot.*:
+    ignore:zmq.eventloop.ioloop is deprecated in pyzmq.*:DeprecationWarning:jupyter_client.*:
+    ignore:`BqplotScatterLayerState` is deprecated and will be removed in a future version.*:DeprecationWarning:glue_jupyter.bqplot.scatter.*:

(though maybe we should better add a pytest.warns context to our own glue_jupyter.bqplot.scatter tests).