I'm using DSpace-CRIS 5.10 and clicking 'Add More' adds a single addition field. I don't see any delete button unless the field is populated, then the 'Remove Entry' button is displayed; clicking it does delete the field. Also, if I click a different 'Add More' button and the field has not been populated, it is removed.
<field>
<dc-schema>dc</dc-schema>
<dc-element>contributor</dc-element>
<dc-qualifier>author</dc-qualifier>
<repeatable>true</repeatable>
<label>Authors</label>
<input-type>onebox</input-type>
<hint>Enter the names of the authors of this item in the form Surname, Firstname [i.e. Smith, Josh or Smith, J].</hint>
<required></required>
</field>