Windows build changed to one done by the datalad-extensions project using Github actions

This is a cleaner build than on Jenkins because the whole environment setup
is handled by the CI config, at least up to the point of "get a random bag
of Windows bytes".

Also, the Jenkins autobuilder has been intermittently failing for a long
time, not due to any problem with git-annex but just a failure to clean up
directories.

Also, this build runs the test suite, and it is (mostly) passing. Test
suite always failed in the jenkins environment.

Also, this build includes libmagic.

Here is the build workflow used by github actions:
https://github.com/datalad/datalad-extensions/blob/master/.github/workflows/build-git-annex-windows.yaml
The libmagic build has its own workflow:
https://github.com/datalad/file-windows/blob/master/.github/workflows/build.yml

(Also cleaned up some windows build cruft I don't use anymore.)

There is no build-version file to link to. I've opened a todo requesting
one: https://github.com/datalad/datalad-extensions/issues/55

standalone/windows/build-simple.sh

@@ -1,16 +0,0 @@
-#!/bin/sh
-# Script to build git-annex on windows. Run by build.bat
-
-set -e
-set -x
-
-PATH="/c/Program Files/Git/cmd:/c/Program Files/NSIS:$PATH"
-
-stack setup
-stack build --dependencies-only
-
-# Build git-annex
-stack build
-
-# Build the installer
-stack runghc --package nsis Build/NullSoftInstaller.hs

standalone/windows/build.sh

@@ -1,71 +0,0 @@
-#!/bin/sh
-# 
-# This script is run by the jenkins autobuilder, in a mingw environment,
-# to build git-annex for Windows.
-
-set -x
-set -e
-
-PATH="/cygdrive/c/git/cmd:/cygdrive/c/Program Files (x86)/NSIS/Bin:/cygdrive/c/Program Files (x86)/NSIS:/usr/local/bin:/usr/bin:/cygdrive/c/Users/jenkins/AppData/Roaming/local/bin:$PATH"
-
-# Run a command with the cygwin environment available.
-# However, programs not from cygwin are preferred.
-withcyg () {
-	PATH="$PATH:/c/cygwin/bin" "$@"
-}
-
-# Prefer programs from cygwin.
-withcygpreferred () {
-	PATH="/c/cygwin/bin:$PATH" "$@"
-}
-
-# This tells git-annex where to upgrade itself from.
-UPGRADE_LOCATION=http://downloads.kitenet.net/git-annex/windows/current/git-annex-installer.exe
-export UPGRADE_LOCATION
-
-# This can be used to force git-annex to build supporting a particular
-# version of git, instead of the version installed at build time.
-#FORCE_GIT_VERSION=1.9.5
-#export FORCE_GIT_VERSION
-
-# Don't allow build artifact from a past successful build to be extracted
-# if we fail.
-rm -f git-annex-installer.exe
-rm -f git-annex.exe
-rm -rf dist
-
-# Upgrade stack
-stack --version
-#stack upgrade --force-download
-#stack --version
-
-# Get stack build environment set up before trying to build any binaries.
-stack setup
-stack build --only-dependencies
-
-# Update version info for git rev being built.
-mkdir -p dist
-stack ghc --no-haddock Build/BuildVersion.hs
-./Build/BuildVersion > dist/build-version
-
-# Build git-annex
-stack install -j 1 --no-haddock --local-bin-path .
-
-# Build the installer
-withcygpreferred stack ghc --no-haddock \
-	--package nsis Build/NullSoftInstaller.hs
-./Build/NullSoftInstaller
-
-# Test git-annex
-# The test is run in c:/WINDOWS/Temp, because running it in the autobuilder
-# directory runs afoul of Windows's short PATH_MAX.
-PATH="$(pwd):$PATH"
-export PATH
-mkdir -p c:/WINDOWS/Temp/git-annex-test/
-cd c:/WINDOWS/Temp/git-annex-test/
-rm -rf .t
-
-# Currently the test fails in the autobuilder environment for reasons not
-# yet understood. Windows users are encouraged to run the test suite
-# themseves.
-#withcyg git-annex.exe test || true