[vm] Remove unused RegularStackTraceBuilder
[vm] Remove unused RegularStackTraceBuilder

TEST=cleanup
Change-Id: I22d0017544ab23ccb359b42e46e3681ba72093f6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/182662
Commit-Queue: Alexander Markov <239e774fd29abc1267878f57afe1a8a03e0ca887@google.com>
Reviewed-by: Ryan Macnak <d738b7f001baf9789095d7dc549cff6de60b011d@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk