qga/commands-win32.c: Drop the check for _WIN32_WINNT >= 0x0601

All current versions of glib require _WIN32_WINNT set to 0x0601
or higher already, and we also use this value as a minimum in our
osdep.h header file, so there is no way to still compile this code
with an older version of the Windows ABI. Thus we can drop this
check now.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Signed-off-by: Konstantin Kostiuk <kkostiuk@redhat.com>