Remove unused functions

[Josef-Friedrich]

Description

Remove unused functions. Fixes #5103.

The function ex_varassign is never called. The function ex_lvalue is only called by ex_varassign.

To Do

• Documentation. (If you've added a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• Changelog. (Add an entry to docs/changelog.rst to the bottom of one of the lists near the top of the document.)
• Tests. (Very much encouraged but not strictly required.)

[Serene-Arc]

Hi, your PR has failed the formatting test. If you could format your PR, that would be appreciated.

[Josef-Friedrich]

If I run tox locally format_check passes ... strange ...

[Serene-Arc]

I just saw it in another PR too, with the same files. I'll have to investigate but it isn't your PR specifically. Sorry, my mistake.