Remove ".yml" from "uhfHeaderId"

We don't usually include the file name extension in these values, and I suspect the build turns these YAML files into JSON.

Author: garycentric

Outlook/docfx.json

@@ -112,7 +112,7 @@
       "recommendations": true,
       "feedback_system": "Standard",
       "hideEdit": true,
-      "uhfHeaderId": "MSDocsHeader-Outlook.yml",
+      "uhfHeaderId": "MSDocsHeader-Outlook",
       "titleSuffix": "Outlook",
       "searchScope": ["Outlook Support"],
       "contributors_to_exclude": [