Get rid of StackChecker

After discussion, we decided that it does more harm than good.

Issues with the StackChecker:

1) Debug builds on linux already use a 50% smaller stack so we would catch getting anywhere near a stack overflow.
2) It broke in the presence of compiler optimizations and sanitizers (which correctly diagnosed it as a buffer overrun).
3) Due to 2, it was disabled on all of our builders.
4) Due to 2, it could never tell us how much stack we actually used in release builds, since optimizations effect stack usage.
5) It would fail or pass based on your choice of compiler.
6) Our response to it failing was always just to raise the limit.