Rely on DEFAULT_DOCUMENT_SUGGESTION page provider for the search

It currently uses default_search with the default_search:ecm_fulltext param but default_search can be easily overridden in Studio.
If it's done in Studio, default_search schema is not used anymore, and ecm_fulltext is system_fulltext.

Relying on DEFAULT_DOCUMENT_SUGGESTION, as the quick search in Web UI, would avoid any issue with redefining the default search.