os.path.realpath will resolve back to the subst paths, leading to
inappropriate current working directories for all downstream hooks.

BUG=1208688

Change-Id: Idfcb0fe4d25ab1317db5aae34663b1017d4c4937
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2893669
Commit-Queue: Dirk Pranke <dpranke@google.com>
Auto-Submit: Robert Liao <robliao@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>