Move `browsingData` extension API out of experimental.

chrome/common/extensions/api/browsingData.json

 [
   {
-    "namespace": "experimental.browsingData",
+    "namespace": "browsingData",
     "types": [
       {
         "id": "RemovalOptions",
         "type": "object",
         "description": "Options that determine exactly what data will be removed.",
         "properties": {
           "since": {
             "type": "number",
             "optional": true,
             "description": "Remove data accumulated on or after this date, represented in milliseconds since the epoch ('Date().GetTime()'). If absent, defaults to 0 (which would remove everything)."
@@ skipping 304 matching lines @@
             "type": "function",
             "description": "Called when websites' WebSQL databases have been cleared.",
             "optional": true,
             "parameters": []
           }
         ]
       }
     ]
   }
 ]