RFC: Remove sqrt_llvm intrinsic

[Keno]

This is more of a "Do we want to move in this direction RFC". As mentioned in #43786,
we currently have three implementations of these intrinsics:

1. The code generated by LLVM for the intrinsic
2. The code LLVM uses for constant folding the intrinsic
3. Our own runtime intrinsic used by the interpreter

This basically removes the third one, which will be required if we want to do
something about #26434 because we just forward these to libm. Of course we'll
still have to do something to teach LLVM how to constant fold these in a manner
compatible with what will actually end up running, but that's a separate issue.

This used to have constprop implications but #43852 will fix that, so this is definitely viable
if we want to go there.

(Of course there's a couple other intrinsics here that are similar, so we'd want to do the same thing).

[vtjnash]

I think it would be generally better to rely more on having correct intrinsics in the interpreter, and move in the opposite direction, rather than relying more heavily on the availability of codegen.