Store collection prefix in mongo adapter, and clean up adapter interface (#1472)

src/ParseServer.js

@@ -84,7 +84,6 @@ class ParseServer {
     appId = requiredParameter('You must provide an appId!'),
     masterKey = requiredParameter('You must provide a masterKey!'),
     appName,
-    databaseAdapter,
     filesAdapter,
     push,
     loggerAdapter,
@@ -127,10 +126,6 @@ class ParseServer {
       })
     }
 
-    if (databaseAdapter) {
-      DatabaseAdapter.setAdapter(databaseAdapter);
-    }
-
     if (databaseOptions) {
       DatabaseAdapter.setAppDatabaseOptions(appId, databaseOptions);
     }