Fix suffixed venv uninstall, and fix suffixed venv install summary.

[itsayellow]

• I have added an entry to docs/changelog.md

Summary of changes

Closes #652 .

On non-symlinked filesystems like typical Windows filesystems, pipx didn't actually delete apps in the local binary dir associated with a suffixed venv. This fixes that.

Also, when summarizing an install, on a non-symlink filesystem (Windows) we would normally not properly handle the installed binaries, reporting each app with (symlink missing or pointing to unexpected location)

Also updated tests to test the functionality that we now do correctly.

Test plan

On Windows!

Install

This PR:

> pipx install pycowsay --suffix _a
done!
creating virtual environment...
installing pycowsay...
  installed package pycowsay 0.0.0.1 (pycowsay_a), Python 3.9.1
  These apps are now globally available
    - pycowsay_a.exe

pipx 0.16.1.0

> pipx install pycowsay --suffix _a
  Overwriting file C:\Users\mclapp\.local\bin\pycowsay_a.exe with C:\Users\mclapp\.local\pipx\venvs\pycowsay-a\Scripts\pycowsay.exe
done!
creating virtual environment...
installing pycowsay...
  installed package pycowsay 0.0.0.1 (pycowsay_a), Python 3.9.1
    - pycowsay_a.exe (symlink missing or pointing to unexpected location)

Uninstall

This PR:

> pipx uninstall pycowsay_a
uninstalled pycowsay_a!
> ls ~/.local/bin/pycowsay_a.exe
ls: cannot access '/c/Users/mclapp/.local/bin/pycowsay_a.exe': No such file or directory

pipx 0.16.1.0

> pipx uninstall pycowsay_a
uninstalled pycowsay_a!
> ls ~/.local/bin/pycowsay_a.exe
/c/Users/mclapp/.local/bin/pycowsay_a.exe*