remove turbotrace from webpack codepath (#71359)
Closes PACK-3356
### What?
We previously supported a flag `experimental.turbotrace` which would opt in to using turbo-tasks powered machinery for performing the tasks that were previously handled by node-file-trace. There was a bifurcation where both turbopack and webpack would use either node-file-trace or the new turbotrace which lead to untested code paths. This never really gained traction on the webpack side and, with the decision to move turbotrace and nft generation directly into the critical path of a turbo build (as opposed to a post-processing step) is obsolete for turbopack. We rip it out.
### Why?
See above
### How?
Remove the flag, and the code path branches that refer to it. I opted to keep some formatting to preserve the diff but may refactor the now-rustless code later as there is still some control flow that is unnecessary.
