Fix undo after non-last port removal in `VisualShaderNodeExpression`

scene/resources/visual_shader.cpp

@@ -3402,7 +3402,6 @@ bool VisualShaderNodeGroupBase::is_valid_port_name(const String &p_name) const {
 }
 
 void VisualShaderNodeGroupBase::add_input_port(int p_id, int p_type, const String &p_name) {
-	ERR_FAIL_COND(has_input_port(p_id));
 	ERR_FAIL_INDEX(p_type, int(PORT_TYPE_MAX));
 	ERR_FAIL_COND(!is_valid_port_name(p_name));
 
@@ -3478,7 +3477,6 @@ bool VisualShaderNodeGroupBase::has_input_port(int p_id) const {
 }
 
 void VisualShaderNodeGroupBase::add_output_port(int p_id, int p_type, const String &p_name) {
-	ERR_FAIL_COND(has_output_port(p_id));
 	ERR_FAIL_INDEX(p_type, int(PORT_TYPE_MAX));
 	ERR_FAIL_COND(!is_valid_port_name(p_name));