Remove unused import.

[garthk]

_virtualenv.py doesn't need to import __future__.annotations, as it has none.

Removing the import:

• Restores the action of the VIRTUALENV_PATCH on Python 3.6

• Eliminates 24 lines of error messages displayed by Python 3.6 when it starts in an environment created by uv:

Error processing line 1 of /tmp/tmp.ENwqZ0oeyb/lib/python3.6/site-packages/_virtualenv.pth:

  Traceback (most recent call last):
    File "~/.pyenv/versions/3.6.15/lib/python3.6/site.py", line 168, in addpackage
      exec(line)
    File "<string>", line 1, in <module>
    File "/tmp/tmp.ENwqZ0oeyb/lib/python3.6/site-packages/_virtualenv.py", line 3
      from __future__ import annotations
                                       ^
  SyntaxError: future feature annotations is not defined

Remainder of file ignored

(Python displays the errors above twice.)

I appreciate the Python team no longer support Python 3.6, but RedHat-style Linux distributions will support Python 3.6 in their /usr/libexec/platform-python until releasever 8 expires in 2029. I'm happy for the community to move on, in general, but don't see the harm in helping those who can't.

I'm not yet sure what in the “remainder of file ignored” is necessary for my project's build, as I haven't yet finished digging that from under Hatch. I'll follow up on #6426 when I do, so we can concentrate on getting to the happy cow.

Test Plan

( set -eu
  export VIRTUAL_ENV="$(mktemp -d)"
  ./target/release/uv venv "$VIRTUAL_ENV" --python=python3.6
  ./target/release/uv pip install cowsay        
  $VIRTUAL_ENV/bin/python -m cowsay --text 'Look, a talking cow!' )

Happy output:

Using Python 3.6.15 interpreter at: ~/.local/bin/python3.6
Creating virtualenv at: /tmp/tmp.VHl4XNi3oI
Activate with: source /tmp//tmp.VHl4XNi3oI/bin/activate
Resolved 1 package in 929ms
Installed 1 package in 17ms
 + cowsay==6.0
  ____________________
| Look, a talking cow! |
  ====================
                    \
                     \
                       ^__^
                       (oo)\_______
                       (__)\       )\/\
                           ||----w |
                           ||     ||

[charliermarsh]

Thanks, while we don't support Python 3.6 (as you mention) this still seems like a reasonable thing to do.

[garthk]

Thanks, @charliermarsh, and thanks @zanieb for fixing the snapshot.