Delete unused MountCrostini fields

Change-Id: I5e3e8fc5c8a4ca0c1bfc1af6dd1076914eab4619
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2483743
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Commit-Queue: Jason Lin <lxj@google.com>
Auto-Submit: Joel Hockey <joelhockey@chromium.org>
Reviewed-by: Jason Lin <lxj@google.com>
Cr-Commit-Position: refs/heads/master@{#818328}

chrome/browser/chromeos/extensions/file_manager/private_api_misc.h

@@ -277,10 +277,6 @@ class FileManagerPrivateMountCrostiniFunction : public LoggedExtensionFunction {
 
   ResponseAction Run() override;
   void RestartCallback(crostini::CrostiniResult);
-
- private:
-  std::string source_path_;
-  std::string mount_label_;
 };
 
 // Implements the chrome.fileManagerPrivate.importCrostiniImage method.