Remove `repyportability` from pure-Repy tests

[aaaaalbert]

Some unit tests for Repy functions and libraries are written in Python and thus have to import repyportability to be able to access the Repy API, use dy_import_..., etc.

The portability stuff should be removed from these tests, and "native" Repy and UTF means of achieving the same thing used:

#pragma repy restrictions.default dylink.r2py
# The above pragma makes dylink's calls available to this program.
modulename = dy_import_module("modulename.r2py")

etc.

(See SeattleTestbed/utf@944be54 where we re-enabled adding arguments other than a restrictions file to the sandbox startup call.)