Remove the use of Pandas' iloc() in  WorldMapViz (#7379)
Remove the use of Pandas' iloc() in  WorldMapViz (#7379)

When the same metric is used in a World Map panel for both bubble size
and an axis (either X or Y), it currently breaks the rendering.

The change in behavior was introduced in:
https://github.com/apache/incubator-superset/commit/71e0c079041c4f955e8529349baa17058e70d256#diff-f451672348fc6071e8d627778bdc4e96L1730

The use of .iloc() is not needed anymore since the code that used
to duplicate the metric is not there anymore.

Should fix #7006
zhouyao1994/incubator-superset,apache/incubator-superset,apache/incubator-superset,mistercrunch/panoramix,apache/incubator-superset,apache/incubator-superset,airbnb/superset,zhouyao1994/incubator-superset,airbnb/superset,airbnb/superset,mistercrunch/panoramix,mistercrunch/panoramix,airbnb/superset,mistercrunch/panoramix,airbnb/caravel,airbnb/caravel,zhouyao1994/incubator-superset,airbnb/caravel,zhouyao1994/incubator-superset,apache/incubator-superset,zhouyao1994/incubator-superset,airbnb/caravel