API: libcrmcommon: deprecate crm_config_error and crm_config_warning

These globals were renamed and retyped in 74278d7b, which mistakenly considered
them internal API. Unfortunately that incompatible API change made it into the
2.0.5 release.

In practice no external code is likely to have used these, so it likely doesn't
matter, but the most appropriate course of action now seems to be to revert the
change and deprecate them instead.