maint: don't mark VIR_WARN or VIR_WARN0 diagnostics for translation

maint: don't mark VIR_WARN or VIR_WARN0 diagnostics for translation

Approximately 60 messages were marked.  Since these diagnostics are
intended solely for developers and maintainers, encouraging translation
is deemed to be counterproductive:
http://thread.gmane.org/gmane.comp.emulators.libvirt/25050/focus=25052

Run this command:
  git grep -l VIR_WARN|xargs perl -pi -e \
    's/(VIR_WARN0?)\s*\(_\((".*?")\)/$1($2/'