Remove enum34+pathlib2

When running in Renovate, uv is incorrectly including enum34 and pathlib2 as
transitive dependencies of pyscss. pyscss only requires these for python
versions below 3.4, but something in the dependency resolver is getting
this wrong.

astral-sh/uv#9217

A fix doesn't seem to be coming imminently.

pyscss is a very old and unmaintained package that we should probably
look to move away from sooner or later.