PERF: Avoid using `@recursive`.

None of the functions decorated with `@recursive` actually need to close
over internal variables, so they can be lifted to become toplevel
recursive functions which avoid the need for an `@recursive` decorator.
(No change was made to the logic of any of the functions.)

As it turns out, the `@recursive` decorator adds a lot of overhead:
`python runtests.py --bench bench_io` reports a ~15-20% perf gain(!)
for `loadtxt` from this PR.  (`_recursive_mask_or` seems less likely to
matter performance-wise, but I also lifted it out for good measure...
and just deleted the decorator's implementation.)

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