Eliminate useless state in Genrou and Gensal

[lukelowry]

Description

Eliminates the algebraic real and imaginary variables that served no purpose. This does not change anything, and the generator still owns its injection current variables.

Proposed changes

• Eliminate Norton current variables

Checklist

• All tests pass.
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• [ x] The new code follows GridKit™ style guidelines.
• N/A There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.
• N/A The CHANGELOG.md has been updated to reflect the changes. If this is a minor PR that is part of a larger fix already included in the file, state so.

Further comments

The documentation was already in the cleaner form, not sure when they diverged

[nkoukpaizan]

A few tests are failing. Likely the ones using the output callback lambda with hard-coded variable indices. We really need to remove those. CC @PhilipFackler