[FilesApp] Remove a incorrect comment

This comment refers to FilesApp since before it was turned into a chrome
component app, and mislead me and others, and is plain wrong these days.
Remove it.

Bug: None
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ide0b7bffb98e82284adc66120ffd0babc22085ea
Reviewed-on: https://chromium-review.googlesource.com/963142Reviewed-by: Sasha Morrissey <sashab@chromium.org>
Reviewed-by: Naoki Fukino <fukino@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543301}

ui/file_manager/file_manager/manifest.json

@@ -16,7 +16,6 @@
     "256": "common/images/icon256.png"
   },
   "permissions": [
-    // Comment out chrome:// permissions to debug on a desktop browser.
     "chrome://extension-icon/",
     "chrome://resources/",
     "chrome://theme/",