util: remove OOM error log from virGetHostnameImpl()

util: remove OOM error log from virGetHostnameImpl()

The strings allocated in virGetHostnameImpl() are all allocated via
g_strdup(), which will exit on OOM anyway, so the call to
virReportOOMError() is redundant, and removing it allows slight
modification to the code, in particular the cleanup label can be
eliminated.

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>