Remove deprecated DatabaseClient, connectionfactory package and other deprecated code

Removal of the connectionfactory package and deprecated core classes that were migrated into Spring Framework R2DBC.

Closes #712

Author: mp911de

src/main/asciidoc/reference/mapping.adoc

@@ -283,9 +283,9 @@ public class PersonWriteConverter implements Converter<Person, OutboundRow> {
 
   public OutboundRow convert(Person source) {
     OutboundRow row = new OutboundRow();
-    row.put("id", SettableValue.from(source.getId()));
-    row.put("name", SettableValue.from(source.getFirstName()));
-    row.put("age", SettableValue.from(source.getAge()));
+    row.put("id", Parameter.from(source.getId()));
+    row.put("name", Parameter.from(source.getFirstName()));
+    row.put("age", Parameter.from(source.getAge()));
     return row;
   }
 }