Summary and Description are mandatory fields in Mantis that can't be removed by configuration.
Other fields can be removed by using option bug_report_page_fields https://www.mantisbt.org/docs/master/en-US/Admin_Guide/html-desktop/#admin.config.fields

You would have to change source of Mantis or write a plugin to get what you want.

Hiding description is a known feature request, see 0011472.
Hiding summary is a questionable request and would require a lot more changes as there are quite a lot of places where summary is displayed and displaying an empty summary would not make sense.