Delete nodeCount attribute of NodeBreakerView network

[miovd]

• Do you want to request a feature or report a bug?
  Evolution? but it will also solve a bug

• What is the current behavior?
  When a Connectable is removed from a voltage level, the vertex is removed if it is isolated. When we export the network to an XML, and import the file, the nodeCount can be lesser than the index of a vertex. Then, an exception is thrown.

• What is the expected behavior?
  The nodeCount attribute will be deleted (not present anymore in the XIIDM file.

• What is the motivation / use case for changing the behavior?
  This attribute was supposed to be used to allocate a certain amount of vertices but it is not so useful in the end... Deleting it would solve the issue.

• Please tell us about your environment:

  • PowSyBl Version: 3.2.0-SNAPSHOT