[X86] Remove some uarch tuning flags from KNL that look to have been inherited...

[X86] Remove some uarch tuning flags from KNL that look to have been inherited from SNB/IVB incorrectly

KNL is based on a modified Silvermont core so I don't think these features apply. I think the LEA flag is probably also wrong, but I'm less sure as I barely understand the 3 LEA flags we have currently.

Differential Revision: https://reviews.llvm.org/D53671

llvm-svn: 345285