Remove Obsolete SentryOptions.EnableTracing

[jamescrosswell]

This is obsolete:

sentry-dotnet/src/Sentry/SentryOptions.cs

Lines 803 to 804 in b2d6162

	[Obsolete("Use TracesSampleRate or TracesSampler instead")]
	public bool? EnableTracing { get; set; }

Documentation will need updating as well.