Remove gclient_variables from linux_license.json (#49766)

The `gclient_variables` has never been used and this is to unblock a recipes CL: https://flutter-review.googlesource.com/c/recipes/+/53902

Part of flutter/flutter#141461

Author: keyonghan

ci/builders/standalone/linux_license.json

@@ -4,9 +4,6 @@
         "os=Linux"
     ],
     "cas_archive": false,
-    "gclient_variables": {
-        "download_android_deps": false
-    },
     "name": "licenses",
     "tests": [
         {