Geometry Nodes: don't show warning in modifier with multiple geometry inputs

Simon mentioned that this gets in the way more than it helps. No geometry
sockets currently show up in the modifier panel. People may build node groups
that have multiple geometry inputs that can be used when the group is used
as node instead of as modifier.

In the future we could also allow e.g. choosing an object to pass into a geometry
socket. That has the problem that we'd also have to duplicate other functionality
of the Object Info node (original vs. relative space).

source/blender/modifiers/intern/MOD_nodes.cc

@@ -1280,9 +1280,6 @@ static void check_property_socket_sync(const Object *ob, ModifierData *md)
       BKE_modifier_set_error(ob, md, "Node group's geometry input must be the first");
     }
   }
-  else if (geometry_socket_count > 1) {
-    BKE_modifier_set_error(ob, md, "Node group can only have one geometry input");
-  }
 }
 
 static void modifyGeometry(ModifierData *md,