Removed double call to ConnectorRegistry.sources (#4448)
Removed double call to ConnectorRegistry.sources (#4448)

Removing the double call didn't cause any adverse effects upon removal. If required, a comment motivating the double call should be added.
dmigo/incubator-superset,airbnb/superset,airbnb/superset,airbnb/caravel,airbnb/superset,dmigo/incubator-superset,apache/incubator-superset,zhouyao1994/incubator-superset,mistercrunch/panoramix,timifasubaa/incubator-superset,airbnb/superset,mistercrunch/panoramix,apache/incubator-superset,timifasubaa/incubator-superset,zhouyao1994/incubator-superset,airbnb/caravel,airbnb/caravel,mistercrunch/panoramix,zhouyao1994/incubator-superset,timifasubaa/incubator-superset,apache/incubator-superset,apache/incubator-superset,airbnb/caravel,mistercrunch/panoramix,dmigo/incubator-superset,zhouyao1994/incubator-superset,zhouyao1994/incubator-superset,dmigo/incubator-superset,timifasubaa/incubator-superset,apache/incubator-superset