Revert "add StorageOperationException to warn users when they try to …

…edit a read-only file"

This reverts commit d34e230.

src/seedu/addressbook/Main.java

@@ -111,9 +111,6 @@ private CommandResult executeCommand(Command command)  {
             CommandResult result = command.execute();
             storage.save(addressBook);
             return result;
-        } catch (StorageOperationException e) {
-            ui.showToUser("StorageOperationException: you are modifying a READ-ONLY file");
-            return new CommandResult("");
         } catch (Exception e) {
             ui.showToUser(e.getMessage());
             throw new RuntimeException(e);