Avoid locale-dependent output in numericlocale check.

Avoid locale-dependent output in numericlocale check.

I'd forgotten that in the buildfarm, parts of the regression tests
may run with psql exposed to a non-default LC_NUMERIC setting.
Hence we can't assume that C locale prevails, nor is there any
accessible way to force the setting for this single test step.
Lobotomize the test case added by commit 9a98984f4 so that it covers as
much as we can of print.c without having any locale-varying output.