Remove unnecessary permission check in task execution from Files.app.

file_tasks::ExecuteTask is called either from
- ExecuteFileTaskForUrl, which always called GrantFileSystemAccessToFileBrowser beforehand, or
- fileBrowserPrivate.executeTask, which is used only from File manager that we always grant permission.

Hence, the check should just always pass.

BUG=337705

Review URL: https://codereview.chromium.org/148383007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247512 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247512