rfc: remove dtrace & etw support

[bnoordhuis]

Do people actually use this? The commit history of the last ~5 years is full of mechanical changes but nothing that suggests actual user feedback, whether bug reports or feature requests. Some of the files haven't been touched since 2012!

The dtrace supports add a great deal of complexity to the build and makes upgrades harder. The etw support in turn leans heavily on the dtrace infrastructure. Ceteris paribus, I'd like to remove both.

cc @cjihrig - maybe you know?

[cjihrig]

I'm not aware of anyone using them or maintaining them - though I could be wrong.