Remove substDealias

[smarter]

Does not seem to be needed anymore.

[smarter]

test performance please

[dottybot]

performance test scheduled: 112 job(s) in queue, 1 running.

[dottybot]

Performance test finished successfully:

Visit http://dotty-bench.epfl.ch/4243/ to see the changes.

Benchmarks is based on merging with master (4c8a2bd)

[odersky]

I am not sure. SubstDealias was needed when we modeled parameters as refinements. But inprinciple the same configurations could arise through explicit refinements. How do we know
this cannot lead to problems? I am worried about scenarios like

[foo := bar]  P { type T = foo } # T

Oh I see, that will in fact replace the foo and we are good. So let's try again:

val x: P { type T = foo }
[foo := bar] x.T

What about this one?

[smarter]

Hmm, but then just dealiasing does not seem to be enough to handle all cases, e.g. what about:

val x: P { type T = foo }
type S <: x.T
[foo := bar] S

[odersky]

@smarter Good point. Can we construct a test case out of this, or is there something else that means we don't substitute in situations like this? If we can't construct a test case I agree we should drop substDealias anyway in order to fail faster.