Revert "Sheriff: Disable session.RetrieveActiveSessions"

This reverts commit abaf2f5e.

Reason for revert: Increased timeout for CreateVault in tast tests, it should fix the issue.

Original change's description:
> Sheriff: Disable session.RetrieveActiveSessions
> 
> TBR=mnissler@chromium.org
> TBR=hidehiko@chromium.org
> 
> Bug: 1117324
> Change-Id: Iec44ae22a5c0452f9b6489c9e0c567e957c68b8b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2359877
> Reviewed-by: Fergus Dall <sidereal@google.com>
> Commit-Queue: Fergus Dall <sidereal@google.com>
> Cr-Commit-Position: refs/heads/master@{#798951}

TBR=hidehiko@chromium.org,mnissler@chromium.org,sidereal@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1117324
Bug: 1116379
Change-Id: Ifa20b34513c09a2a3bbf3ee17865b92229a52820
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2362818Reviewed-by: Victor-Gabriel Savu <vsavu@google.com>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Fergus Dall <sidereal@google.com>
Commit-Queue: Victor-Gabriel Savu <vsavu@google.com>
Cr-Commit-Position: refs/heads/master@{#799575}

chromeos/BUILD.gn

@@ -322,9 +322,6 @@ if (is_chromeos_device) {
 
       # crbug.com/1114752
       "arc.ContainerMount",
-
-      # crbug.com/1117324
-      "session.RetrieveActiveSessions",
     ]
   }