We were adding paths for the error pages in two places so one of them
simply wasn't being used. The lms urls.py also covered the 429 wich the
static_templates_view urls.py did not cover. We don't need both and we
need the definition of the handlerNNN variables in urls.py to override
the default django error views so I'll leave just those.
I also made the `exception` parameter for the `render_404` function
optional by adding a default value. We don't use the exception when
rendering the 404 page but the exception argument is a part of the
default method signature for the function that `render_404` replaces so
I didn't want to remove it and cause issues when django tries to call
this function.
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