Deprecate CoreCH algorithm

[TheMarex]

Since we now have feature parity with MLD, there is no reason to keep CoreCH around - it is slower and has less features then MLD.

Removing CoreCH will let us remove the following flags for osrm-contract:

• core-factor
• use-level-cache
• .level file
• .core file

We might be able to remove the code for handling CoreCH by automatically falling back to a plain CH (and printing warnings).

[danpat]

Some of these changes already happened for the 5.12 release - moving this to the 5.13 release so the deprecation can be deliberate.