Multiple choices with only one choice

[alexbruy]

After writing the XML, some multiple choices have a single choice.

Some applications are split using different predefined values of a parameter (eg. mode, filter....; Segmentation is split using the parameter "filter").
But this parameter is still considered as a parameter. It was a choices which has only one choice.
Some other parameters choices are removed during the XML creation. This can also bring a multiple choices with a single choice.

These parameters should be removed and their name and value should be added to the node cli_args_template #6.

Moved from QGIS bugtracker https://issues.qgis.org/issues/14555