Update virtual environment removal to delete `pyvenv.cfg` last (#14808)
An alternative to https://github.com/astral-sh/uv/pull/14569
This isn't a complete solution to
https://github.com/astral-sh/uv/issues/13986, in the sense that it's
still "fatal" to `uv sync` if we fail to delete an environment, but I
think that's okay — deferring deletion is much more complicated. This at
least doesn't break users once the deletion fails. The downside is we'll
generally treat this virtual environment is valid, even if we nuked a
bunch of it.
Closes https://github.com/astral-sh/uv/issues/13986