Before crrev.com/c/2876082, DEPOT_TOOLS_METRICS=0 was the
env var used to disable metrics collection.

Bug: b/191388102
Change-Id: I0db9d034562f2eb1afb53818b3853cef50c09826
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2980230
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Jack Neus <jackneus@google.com>
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Jack Neus <jackneus@google.com>