Revert "matplotlib-inline: Don't depend on matplotlib -> smaller ipython closure"

Meant to go to staging, not staging-next

This reverts commit f38610c09b.

pkgs/development/python-modules/matplotlib-inline/default.nix

@@ -1,4 +1,5 @@
 { lib, buildPythonPackage, fetchPypi
+, matplotlib
 , traitlets
 
 # tests
@@ -15,6 +16,7 @@ buildPythonPackage rec {
   };
 
   propagatedBuildInputs = [
+    matplotlib # not documented, but required
     traitlets
   ];