crt: tests: t_assert: do not set `stderr` to Unicode translation mode

By default, `assert` macro calls CRT function `_assert`; this function
does not work when `stderr` is set to Unicode translation mode.

This test was added in b2c3c92b542df57ed8bfcd798928692e94a35308 to
test mingw-w64 wrapper for `_assert`, which was added to make it work
in cases when `stderr` wsa set to Unicode translation mode.

With this change, t_assert becomes a simple test for `assert` macro.

Signed-off-by: Kirill Makurin <maiddaisuki@outlook.com>
Signed-off-by: LIU Hao <lh_mouse@126.com>