Remove a custom command for the system. If the argument does not specify a valid custom command this call does nothing.
Built-in commands cannot be removed. (However they can be greyed out in Softimage's Menus. See
Command.Enabled.)
Note: This command does not delete the implementation of the command. It simply removes the reference to the command
from Softimage's command list.
To remove a custom command that is defined as part of a self-installed plug-in remove the script file or dll rather
than calling this method. Similarly, this method cannot be used to remove custom commands that are installed as part
of an add-on.