remove non-standard File System related API

follow mdn/content#15815

Author: yin1999

files/zh-cn/_wikihistory.json

@@ -12777,13 +12777,6 @@
       "ziyunfei"
     ]
   },
-  "Web/API/FileRequest": {
-    "modified": "2019-03-23T23:02:38.410Z",
-    "contributors": [
-      "teoli",
-      "phoenix_in_the_sky"
-    ]
-  },
   "Web/API/FileSystem": {
     "modified": "2019-03-23T22:48:51.462Z",
     "contributors": [