Removed plot from two examples, in order that runtests.jl works

[MartinOtter]

Due to a bug in ModiaMath (see issue), ModiaMath.plot on arrays does not work. In order that runtests.jl works, temporarily deactivated ModiaMath.plot(...) calls that plot an array:

• Modia/examples/LinearSystems.jl
• Modia/test/models/TestSpatialDiscretization.jl

[HildingElmqvist]

Strange. I was able to previously run all tests successfully.

[MartinOtter]

The reason was the ModiaMath version 0.2.2 that I released yesterday. Here I included the feature that plots can be added to existing figures, without clearing the previous content. Hereby, I had to change the way how the legend of the plots is built.

I do not fully understand the reason, but my guess is that previously when an array was plotted in Modia (say vector x with 5 elements), then 5 lines are plotted and the legend was just "x" (so only of limited use). Due to the change in ModiaMath with the legend handling, this did no longer work (because the length of the legend vector is now assumed to have the same length as the number of array elements).

I know how to fix this in ModiaMath, but will not manage to do it today.

[MartinOtter]

Re-added the plot commands with commit 0ec2bd4
(works with ModiaMath 0.2.4).