Drop support for numpy 1.16

We said we would do that some time ago and havent.

Likely for 7.24

setup.py

@@ -181,7 +181,7 b' extras_require = dict('
         "pygments",
         "nbformat",
         "ipykernel",
-        "numpy>=1.16",
+        "numpy>=1.17",
     ],
     terminal=[],
     kernel=["ipykernel"],