Remove pred from compat.any/all

This makes it compatible with the python builtin, and we can even use
the builtin when running under the right version of python. The all and
any functions are renamed to _all and _any, so that they can be tested,
and (non)existing unittests are updated (translation: there are no unit
tests, so none are updated).

This patch also moves the code deciding which partial to use next to
the definition of the _partial function, rather than after TryToRoman.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>