Configurations/windows-makefile.tmpl: simplify install-path "flavour"-ing.

$target{build_scheme} consists of fixed number of elements with 3rd
element denoting VC install-path "flavour", i.e. where to install things.
Instead of looking at 3rd, let's look at last. This allows to override
flavour from template in a simple way.

Configurations/10-main.conf: define generic "flavour" in VC-common
template. Since VC-W32 was the only recognized "flavour", remove
"flavour" definitions from all targets/templates, but VC-WIN32. And
rename VC-W32 to VC-WOW.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5502)