remove voltage step without angles

[Sander-Timmerman]

Fixes issue: # name and number of the issue

Changes proposed in this PR include:

Here you can elaborate on the chosen solution strategy, which changes did you make and which goal do they serve. Perhaps also which things are you still unsure of.

• The voltage step without angles now gives an error. So we should remove that
• ..

Could you please pay extra attention to the points below when reviewing the PR:

Here you can point out modules or complex implementation that require special attention, .e.g have a look at module foo.py and bar.py.

• Did I not miss any reference to the step without voltage angles
• We now don't use update_data anymore in the state estimation workshop, should be replace this by anything else?
• ..

[mgovers]

TODO: also update the solutions in accordance to the workshop itself

[figueroa1395]

Since assignment 3 now only contains an error and not a task, we may want to put them together (3 and 4) back again such that the assignment is to fix the error. However, it is probably better to address the above: How are we going to handle this potentially breaking change.

[figueroa1395]

Again seeing differences where I don't think there should be. You think is worth taking a look?

[Sander-Timmerman]

And this is because of different rounding

[figueroa1395]

Just triple checking that this expected before resolving (cc @mgovers), maybe you can elaborate a bit more so it is documented somewhere for future reference? Since validation test cases remain intact, I don't expect this to be an issue, but just want to make sure. If you are sure this is fine, feel free to resolve.