use WMCore.Configuration (fix #5119)

[ddaina]

No description provided.

[mapellidario]

The module https://github.com/dmwm/CRABClient/blob/master/src/python/CRABClient/WMCoreConfigWrapper.py has not been changed. Are we still using it? Should we remove it? Or should we change the import in there, too?

[ddaina]

we should not use it anymore. what we do instead: https://github.com/cms-sw/cmsdist/pull/7470/files#diff-001d3e278ac2167f3587cbba653377a815386e1e2b44a1c699f498cfcad9f5f8R53 i.e. copy original configuration from here https://github.com/dmwm/CRABClient/blob/master/src/python/CRABClient/WMCoreConfiguration.py to WMCore/ folder during build process

see notes from Stefano: https://github.com/dmwm/CRABClient/releases/tag/v3.211125

[belforte]

We will revisit this as "cleanup" once dust settles on the python3 migration and we review the situation.
Given enough time it is conceivable to go back to "stop importing from WMCore", e.g. we should start by not putting the config in the .requestcache pickle file, wait one months for all task around to have the new files and go on.
Or we find a way to make both fromWMcore and fromCRABClient work at same time and rather move the warning from the wrapper into the WMCore/Configution.py ...

So let's keep this file around for a while.