M1 mac seems to have capacity to build with higher parallelism.
This also remove limit in macOS.

Bug: 1317620
Change-Id: I4460915c405cbb27ed977dcee631adb8753f2335
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3596361
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Junji Watanabe <jwata@google.com>
Reviewed-by: Fumitoshi Ukai <ukai@google.com>
Reviewed-by: Philipp Wollermann <philwo@google.com>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>