Mark BrowserSwitcherUseIeSitelist policy Windows-only

Bug: 904840
Change-Id: I49876ee13a190b0b257197d31cd93230778a0e08
Reviewed-on: https://chromium-review.googlesource.com/c/1311079
Commit-Queue: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607616}

components/policy/resources/policy_templates.json

@@ -13782,7 +13782,7 @@
         'dynamic_refresh': False,
         'per_profile': True,
       },
-      'supported_on': ['chrome.*:71-'],
+      'supported_on': ['chrome.win:71-'],
       'caption': '''Use Internet Explorer's SiteList policy for Legacy Browser Support.''',
       'tags': [],
       'desc': '''This policy controls whether to load rules from Internet Explorer's SiteList policy.