Removing a filter generates an invalid query

[santilococo]

Describe the bug
When you search with more than one filter and remove one from the top (not from the menu on the left), a malformed SOLR URL will be created. It incorrectly removes ",equals" from the URL, resulting in an invalid SOLR query. This happened in DSpace 7.3 and in the DSpace demo (7.4).

To Reproduce
Steps to reproduce the behavior:

1. Search with two or more filters:
   

2. Remove one filter from the top (click the X on the chip/badge):
   

3. Then:
   

Expected behavior
Do not remove the ,equals.