tests: portability: cmsis_rtos_v2: do not disable 64-bit timeouts

Some code that automatically gets embedded on some platforms relies
on having `CONFIG_TIMEOUT_64BIT` enabled.
Do not force disabling that Kconfig option in the test configuration,
as that will make the test fail to compile on those platforms.

Signed-off-by: Tomi Fontanilles <tomi.fontanilles@nordicsemi.no>