[mac/arm] pull python3 binary in cipd bootstrap now that it exists

With this, it's possible to run some things without

  export VPYTHON_BYPASS="manually managed python not supported by chrome operations"

on an arm mac, such as `git cl upload` -- this CL was uploaded
from my M1 MBP :)

(Presubmits need py2 which we don't have yet, but with
`--bypass-hooks` it works.)

Bug: 1103326,1184767,1103236
Change-Id: I46f5b880dfd72b8d811d39b43311fdee17ccad3e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2858534
Commit-Queue: Dirk Pranke <dpranke@google.com>
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>

bootstrap/manifest.txt

@@ -21,9 +21,8 @@ $VerifiedPlatform windows-amd64 linux-amd64 mac-amd64
 @Subdir python
 infra/3pp/tools/cpython/${os}-${arch=amd64} version:2.7.17.chromium.22
 
-# TODO(https://crbug.com/1103326): Remove `=amd64` once mac/arm64 python3 exists
 @Subdir python3
-infra/3pp/tools/cpython3/${os}-${arch=amd64} version:2@3.8.9.chromium.14
+infra/3pp/tools/cpython3/${platform} version:2@3.8.9.chromium.14
 
 # TODO(https://crbug.com/1184766): Remove `=amd64` once mac/arm64 git exists
 @Subdir git

bootstrap_python3

@@ -29,11 +29,6 @@ function bootstrap_python3 {
       -root "$BOOTSTRAP_PATH"
 
   BOOTSTRAP_PYTHON_BIN="${BOOTSTRAP_PATH}/python3/bin/python3"
-  if [[ ! -x "$BOOTSTRAP_PYTHON_BIN" && $(uname -sm) == "Darwin arm64" ]]; then
-    # There's no CIPD python3 package on mac/arm64. fall back to system python3.
-    # TODO(https://crbug.com/1103326): Remove once mac/arm64 python3 exists.
-    BOOTSTRAP_PYTHON_BIN=python3
-  fi
   "$BOOTSTRAP_PYTHON_BIN" "bootstrap/bootstrap.py" --bootstrap-name "$BOOTSTRAP_PATH"
 
   cd - > /dev/null