[analyzer] Website: update lists of potential and actual checkers.

- memory.MismatchedDelete, memory.MultipleDelete, and memory.DeallocateNonPtr
  are complete (unix.MismatchedDeallocator and cplusplus.NewDelete)
- Per discussion on the mailing list, different.UnaryPlusWithUnsigned has
  dubious value; remove it.
- Add potential checker ctordtor.PlacementSelfCopy per an internal bug report.
- core.AttributeNonNull is now core.NonNullParamChecker, though no one should
  be depending on this name anyway.