Revert "Adding Supplement:Apache-2.0 to chromium license allowlist."

This reverts commit 9dd0755b69.

Reason for revert: 'Supplement:Apache-2.0' is considered to be allowed, but is not technically a valid SPDX identifier.

Original change's description:
> Adding Supplement:Apache-2.0 to chromium license allowlist.
>
> The 'Supplement:Apache-2.0' contains the full license text and is the preferred version over just 'Apache-2.0'.
>
> Change-Id: Ie4566ffdcd20771a0170190270d8d45e1b77980d
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6040532
> Reviewed-by: Jordan Brown <rop@google.com>
> Reviewed-by: Rachael Newitt <renewitt@google.com>
> Commit-Queue: Rachael Newitt <renewitt@google.com>
> Auto-Submit: Jordan Brown <rop@google.com>

Change-Id: Ic6529514304b826dbc8840a468bab47321c30471
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6040754
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Jordan Brown <rop@google.com>

metadata/fields/custom/license_allowlist.py

@@ -10,7 +10,6 @@
 ALLOWED_SPDX_LICENSES = frozenset([
     "APSL-2.0",
     "Apache-2.0",
-    "Supplement:Apache-2.0",
     "BSD-2-Clause",
     "BSD-2-Clause-FreeBSD",
     "BSD-3-Clause",