Revert "virthread: Introduce virRWLockInitPreferWriter"
    
    This reverts commit 328bd24443d2a345a5832ee48ebba0208f8036ea.
    
    As it turns out, this is not portable and very Linux & glibc
    specific. Worse, this may lead to not starving writers on Linux
    but everywhere else. Revert this and if the starvation occurs
    resolve it.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
    Reviewed-by: Daniel P. Berrange <berrange@redhat.com>