Retire Symantec CT Logs

The Symantec Log, Symantec 'Sirius' Log, and Symantec 'Vega' Log are
being retired with an effective date of February 16, 2019 with a
timestamp of 1550275200.

Bug: 928879
Change-Id: I8f9a3da420acdda7739662481fe505bc7c46bf3e
Reviewed-on: https://chromium-review.googlesource.com/c/1481606Reviewed-by: Andrew Whalley <awhalley@chromium.org>
Reviewed-by: Nick Harper <nharper@chromium.org>
Commit-Queue: Andrew Whalley <awhalley@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634675}

components/certificate_transparency/data/log_list.json

@@ -264,6 +264,7 @@
    "operated_by": [
     2
    ],
+   "disqualified_at": 1550275200,
    "dns_api_endpoint": "symantec.ct.googleapis.com"
   },
   {
@@ -274,6 +275,7 @@
    "operated_by": [
     2
    ],
+   "disqualified_at": 1550275200,
    "dns_api_endpoint": "symantec-vega.ct.googleapis.com"
   },
   {
@@ -284,6 +286,7 @@
    "operated_by": [
     2
    ],
+   "disqualified_at": 1550275200,
    "dns_api_endpoint": "symantec-sirius.ct.googleapis.com"
   },
   {