Fix bundle size

[rdavison]

Reported in https://github.com/ocaml/v3.ocaml.org/issues/519#issuecomment-914690486

The functor at Pages.MakeSimple may be causing bundle sizes to be too large. The working theory is that webpack is unable to perform its tree-shaking algorithm correctly. @patricoferris demonstrated an example proof-of-concept solution in the linked issue by inlining the functor application, and copying the resulting output over the top of one page, and saw that the bundle size was no longer a problem.