Bug 1623222 - Remove the charset parameter from nsITextToSubURI::UnEscapeURIForUI. r=hsivonen

Only 3 callers are using a non-UTF-8 charset as the first parameter.
* MediaDocument.cpp: This does not make sense because the "filename" part of
  URLs will always be encoded with UTF-8.
* nsContextMenu.js: This is wrong because "mailto:" URLs don't care about the
  document charset.
* Finder.jsm: This caused bug 1623222.

Differential Revision: https://phabricator.services.mozilla.com/D67386

docshell/base/nsDocShell.cpp

@@ -3939,8 +3939,7 @@ nsDocShell::DisplayLoadError(nsresult aError, nsIURI* aURI,
       nsCOMPtr<nsITextToSubURI> textToSubURI(
           do_GetService(NS_ITEXTTOSUBURI_CONTRACTID, &rv));
       if (NS_SUCCEEDED(rv)) {
-        rv = textToSubURI->UnEscapeURIForUI(NS_LITERAL_CSTRING("UTF-8"), spec,
-                                            nextFormatStr);
+        rv = textToSubURI->UnEscapeURIForUI(spec, nextFormatStr);
       }
     } else {
       spec.Assign('?');