Remove 6 of XFAIL(s) in llvm/test/TableGen, since r193736. They have been XPASSing.
Mark 36 tests as XFAIL:vg_leak in llvm/test/TableGen.

In historical reason, tblgen is not strictly required to be free from memory leaks.
For now, I mark them as XFAIL, they could be fixed, though.