Deleting BasicBlockPass/Manager

Hi,

I sent out a patch (D69121) removing the BasicBlockPass, BasicBlockManager and all their dependencies following the patch that cleaned up the instantiations of the BasicBlockPass (rL373254).

The motivation was that the BasicBlockManager was generally unused, untested, was potentially broken (PR42264, PR43429, PR43336, PR42246), and any BasicBlockPass could be updated to be a FunctionPass looping over all BBs.

If you have comments or concerns about this cleanup please let me know.

Best,
Alina

Heads up that this landed in this revision. Updated release notes here.

Best,
Alina