Fix FlatList not working because of the forced flex style attribute

Some testing in Snack showed that the `FlatList` component was not
properly working, the main reason being that the `flex` style attribute
was forced to `1` in the `FlatList` component.  For whatever reason,
when this settings is set, either the Webpreview fail to render the
FLatlist, or the Appetize preview do.

Author: Timothée Vialatoux

packages/core/src/mappings/FlatList.ts

@@ -15,9 +15,6 @@ export const SEED_DATA = {
   description: "A basic List component",
   category: COMPONENT_TYPES.data,
   stylesPanelSections: CONTAINER_COMPONENT_STYLES_SECTIONS,
-  layout: {
-    flex: 1,
-  },
   triggers: [Triggers.OnRefresh, Triggers.OnEndReached],
   props: {
     onRefresh: createActionProp(),