[OpenStaad] Add a Design.DeleteDesignCommand function in open staad.

Currently, using the Design.AssignDesignCommand function to add a design command like "CODE CHECK" is ideal only for one execution using VBA. If you execute the code multiple times, the "CODE CHECK' command is added to the command equal to the number of times you executed the macro. My goal is to automate my analysis that every time a user is updating the model like adding new members, I can just execute a macro to re-apply the "CODE CHECK" to "all members" including the additional members without manually selecting the "CODE CHECK" command and assigning it to view. So, an additional function to delete an existing design command would be a good one. And you could add another function that list all the added commands, so that we can put a logic in our code that if say "CODE CHECK" exists in the commands, I can only delete the "CODE CHECK" command without affecting the other commands.