Remove the special-casing for Files app allowing file_browser_handlers.

Files app has migrated to file_handlers, so allowing it to use
file_browser_handlers is no longer necessary.

Bug: 933674
Change-Id: Ifffadba9c7444516ebd759ecc5fa9246bbd620f8
Reviewed-on: https://chromium-review.googlesource.com/c/1496117
Auto-Submit: Sam McNally <sammc@chromium.org>
Reviewed-by: Ben Wells <benwells@chromium.org>
Commit-Queue: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636722}

chrome/common/extensions/api/_manifest_features.json

@@ -140,17 +140,10 @@
     "channel": "stable",
     "extension_types": ["shared_module"]
   },
-  "file_browser_handlers": [
-    {
-      "channel": "stable",
-      "extension_types": ["extension", "legacy_packaged_app"]
-    },
-    {
-      "channel": "stable",
-      "extension_types": ["platform_app"],
-      "location": "component"
-    }
-  ],
+  "file_browser_handlers": {
+    "channel": "stable",
+    "extension_types": ["extension", "legacy_packaged_app"]
+  },
   "file_system_provider_capabilities": [{
     "channel": "stable",
     "extension_types": ["extension", "platform_app"]