Remove redundant entries in _permissions_features.json

fileSystem's "default_parent" entry has the same fields as some of its
children, so those children's fields don't need to be manually specified.

See chrome/common/extensions/api/_features.md and crrev.com/2939833002.

Bug: 729713
Change-Id: I1eed160c01fb139d1c1b75217e10a343a6308f24
Reviewed-on: https://chromium-review.googlesource.com/575912
Commit-Queue: Michael Giuffrida <michaelpg@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488039}

extensions/common/api/_permission_features.json

@@ -247,16 +247,13 @@
     ]
   }],
   "fileSystem.directory": {
-    "channel": "stable",
-    "extension_types": ["platform_app"]
+    // Inherit from fileSystem's default_parent.
   },
   "fileSystem.retainEntries": {
-    "channel": "stable",
-    "extension_types": ["platform_app"]
+    // Inherit from fileSystem's default_parent.
   },
   "fileSystem.write": [{
-    "channel": "stable",
-    "extension_types": ["platform_app"]
+    // Inherit from fileSystem's default_parent.
   },{
     "channel": "stable",
     "extension_types": ["extension"],
@@ -270,8 +267,6 @@
     ]
   }],
   "fileSystem.requestFileSystem": {
-    "channel": "stable",
-    "extension_types": ["platform_app"],
     "platforms": ["chromeos"]
   },
   "hid": [