Deopt does not throw

Rationale:
"CanThrow" of deopt was possibly misused to prevents some
optimizations. However, the instruction technically cannot
throw an exception, and indeed crashed the graph verifier
for some corner cases. This Cl sets that right.

Bug: 29868356

Test: test-art-host,target
Change-Id: Icb551d3b2935282a70ad673a0544e4fe01104da1