rpc: Don't translate warning messages

But keep translating them in the GUI.
This - necessarily - requires duplication of a few messages.
Alternative take on #7134, that keeps the translations from being wiped.

Also document GetWarnings() input argument.

Fixes #5895.

src/qt/clientmodel.cpp

@@ -158,7 +158,7 @@ enum BlockSource ClientModel::getBlockSource() const
 
 QString ClientModel::getStatusBarWarnings() const
 {
-    return QString::fromStdString(GetWarnings("statusbar"));
+    return QString::fromStdString(GetWarnings("gui"));
 }
 
 OptionsModel *ClientModel::getOptionsModel()