Revert "[analyzer] Remove constraints on dead symbols as part of removeDeadBindings."

Revert "[analyzer] Remove constraints on dead symbols as part of removeDeadBindings."

While we definitely want this optimization in the future, we're not
currently handling constraints on symbolic /expressions/ correctly.
These should stay live even if the SymExpr itself is no longer referenced
because could recreate an identical SymExpr later. Only once the SymExpr
can no longer be recreated -- i.e. a component symbol is dead -- can we
safely remove the constraints on it.

This liveness issue is tracked by <rdar://problem/12333297>.

This reverts r163444 / 24c7f98828e039005cff3bd847e7ab404a6a09f8.

llvm-svn: 164275