Since 6th Jan, 2022, builds on Appveyor are failing because they
cannot find `autoreconf`[1][2].

This should be implemented from `base-devel`, but even with
`base-devel` available the builds are failing. Adding an explicit
require on `autoconf` in the hope that this is fixed.

1: https://ci.appveyor.com/project/vedang/pdf-tools/builds/42114287
2: https://ci.appveyor.com/project/vedang/pdf-tools/builds/42101965

Relates to: #68

- Use VS 2019 image
- Combine pacman install commands
- For some reason, OpenSSL dlls were not copied as dependencies. Update to copy
explicitly. Also remove previously workaround.

I'm making these changes based on reading through the output logs of
the Appveyor code, I don't have any understanding of how mingw64
works.

The go script is deprecated and will be removed in a few months.

https://ci.appveyor.com/project/vedang/pdf-tools/builds/38649076
failed with `python2 not found`, which was the proposed fix in
politza/pdf-tools@628 . My guess is that `python2` now needs to be
explicitly installed in mingw64.

This commit adds an explicit dependency on `mingw-w64-x86_64-python2`
to test this.

Closes politza/pdf-tools@628

... rather than 'python' (issues with Python 3 and Cask on Windows)