Remove AbstractNode::supportsCircuitMode

[pjattke]

The method AbstractNode::supportsCircuitMode is obsolete and its naming is confusing. Its initial intention was to provide a way to distinguish between AST nodes that use the AbstractNode's children/parent vector and those that do not. As now almost all AST nodes use the children vector to store its attributes, the method is not required anymore.

• Adapt CallExternal: Store attributes in AbstractNode's children vector
• Check if any class still does not use the children/parent vectors to store its attributes
  • Check if any class does not overwrite the inherited method AbstractNode::supportsCircuitMode
  • Check if the overwrite of AbstractNode::supportsCircuitMode in any class returns False
  • Check and remove usages of AbstractNode::supportsCircuitMode
• Remove the method AbstractNode::supportsCircuitMode

[AlexanderViand]

CircuitMode is no longer a concept in the new smart-pointer-based ast