Revert "[pgo/mac] disable widevine signing for Mac PGO bots"

This reverts commit 0d501f4f.

Reason for revert: Added it to wrong MB config

Original change's description:
> [pgo/mac] disable widevine signing for Mac PGO bots
> 
> enable_widevine_cdm_host_verification = false was missing from
> GN args for PGO Mac bots, which is causing build failures.
> 
> Bug: 1128810
> Change-Id: I2ccd1db80e80fd983e5f4ef0bd63908281557a04
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2425846
> Commit-Queue: Jeff Yoon <jeffyoon@chromium.org>
> Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
> Auto-Submit: Jeff Yoon <jeffyoon@chromium.org>
> Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#809877}

TBR=liaoyuke@chromium.org,jeffyoon@chromium.org

Change-Id: I5f4beb446367d5110d267b527df39eae12812a35
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1128810
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2427343Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Commit-Queue: Jeff Yoon <jeffyoon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809891}

tools/mb/mb_config.pyl

@@ -2168,7 +2168,7 @@
     ],
 
     'official_goma_mac': [
-      'official', 'goma', 'no_widevine_cdm_host_verification', 'disable_widevine_signing'
+      'official', 'goma', 'no_widevine_cdm_host_verification',
     ],
 
     'official_goma_perf': [
@@ -2685,10 +2685,6 @@
       'gn_args': 'archive_seed_corpus=false',
     },
 
-    'disable_widevine_signing': {
-      'gn_args': 'enable_widevine_cdm_host_verification = false'
-    },
-
     'dx12vk': {
       # TODO(https://crbug.com/1010584): Explicitly enable DirectX 12.
       'mixins': ['enable_vulkan'],