setup exe used to install Electrum to `C:\Program Files (x86)\Electrum`,
but now as the binaries are amd64, we should install to `C:\Program Files\Electrum`.
With this change, based on my experiments, looks like if there is an existing install,
nsis will keep using that path, but if it's a fresh install, it will now use the 64-bit path.
follow-up fcc4e1d387
Before, it was only possible to test commits that are
on Github (pull request or merged). Now, changes can be
tested locally too.
This introduces the risk that a release could be built
containing uncommitted changes which by definition breaks
deterministic builds. Fortunately, this will always be
detected because the version string is created using
`git describe --tags --dirty`.
Also, retire $TARGET variable because it decouples the
build scripts from the commit revision to be built. This
is a problem for deterministic builds.