Since which version is the mining functionality removed from the wallet?
Bitcoin Core removed it in version 0.13.0.  You can see the change log at https://bitcoin.org/en/release/v0.13.0:


  Removal of internal miner
  
  As CPU mining has been useless for a long time, the internal miner has been removed in this release, and replaced with a simpler implementation for the test framework.


For future questions like this, all change logs can be found at https://bitcoin.org/en/version-history.