getControl(), clearOptions() and removeOption() not running on Catalog Tasks or Requested Items

Use form.removeOption instead of g_form.removeOption

Before that use this method:

var form = typeof g_sc_form != "undefined" ? g_sc_form : g_form; 

For more information: https://support.servicenow.com/kb?id=kb_article_view&sysparm_article=KB0547171