Remove the DefinitelyInitializedPlaces analysis.

Its only use is in the `tests/ui/mir-dataflow/def_inits-1.rs` where it
is tested via `rustc_peek_definite_init`.

Also, it's probably buggy. It's supposed to be the inverse of
`MaybeUninitializedPlaces`, and it mostly is, except that
`apply_terminator_effect` is a little different, and
`apply_switch_int_edge_effects` is missing. Unlike
`MaybeUninitializedPlaces`, which is used extensively in borrow
checking, any bugs in `DefinitelyInitializedPlaces` are easy to overlook
because it is only used in one small test.

This commit removes the analysis. It also removes
`rustc_peek_definite_init`, `Dual` and `MeetSemiLattice`, all of which
are no longer needed.

compiler/rustc_span/src/symbol.rs

@@ -1725,7 +1725,6 @@ symbols! {
         rustc_partition_reused,
         rustc_pass_by_value,
         rustc_peek,
-        rustc_peek_definite_init,
         rustc_peek_liveness,
         rustc_peek_maybe_init,
         rustc_peek_maybe_uninit,