Fix bug where the same plot could appear multiple times

[eric-wieser]

Notebook html generated with pyganja output would contain javscript akin to:

function add_graph_to_notebook() { foo(); }
call_soon(() => add_graph_to_notebook());
function add_graph_to_notebook() { bar(); }
call_soon(() => add_graph_to_notebook());

If line 3 runs before soon expires on line 2, then bar() gets called twice, and foo() doesn't get called at all.

This fixes things by not naming the function at all.

It seems the comment about requirejs vs require was wrong - requirejs works in both places.

Fixes pygae/clifford#170