When a query parameter is used twice in search or the same facet is
selected twice in the search input handle it the same way.

- Remove special code for multi-value filter clauses
- Remove special parsing of text facet, which seems to have been
  added by mistake (the space-delimited text field might come from
  the text field being the default remainder field, meaning it takes
  the left-over text in the search box which doesn't match a facet)