Use timespec_get on iOS/tvOS/Catalyst now that we have 13.0 as min version

[akoeplinger]

After #122436 we can get rid of this fallback:

runtime/src/coreclr/utilcode/debug.cpp

Lines 166 to 171 in 67e6e17

	#if defined(HOST_IOS) || defined(HOST_TVOS) || defined(HOST_MACCATALYST) || defined(HOST_ANDROID)
	// timespec_get is only available on iOS 13.0+ and not supported on Android API levels we target, use gettimeofday instead
	struct timeval tv;
	gettimeofday(&tv, nullptr);
	ts.tv_sec = tv.tv_sec;
	ts.tv_nsec = tv.tv_usec * 1000;

[dotnet-policy-service]

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