Here code to remove all table data in a system variable:
//Retrieve the Entire table and parse as a CSV message model
csvModel = qie.parseCSVString(qie.getVariable('testVariable1'));
//set variable back with only the csv column names
qie.setVariable('testVariable1', qie.parseCSVString(csvModel.getNode('*[0]'), true, '"', ',', true, 'UTF-8'));