Removing dynamic loading of ntdll APIs will unnecessarily break building
the tests with older PSDK versions, in particular Windows 7/8 ones. I'm
occasionally use Windows 7 to test things, I'd appreciate if building
under that platform keeps working.

 Isn't this already the case? (i.e. RtlInitUnicodeString in set_env_var() and RtlSetCurrentEnvironment in test_RtlSetCurrentEnvironment())