[md][assembly] Unify coupling Jacobian pattern for cvfe schmes

What this MR does / why does DuMux need it:

Use the same implementation for the coupling jacobian for all cvfe schemes

• is the code you changed and/or the new code you wrote covered in the test suite? (if not, extend the existing tests or write new ones)
• is the list of the header includes complete? ("include what you use")
• all files have to end with a \n character. Make sure there is no \ No newline at end of file comment in "Changes" of this MR.