Remove some last remants of {push,pop}_unsafe!

These macros have already been removed, but there was still some code
handling these macros. That code is now removed.

compiler/rustc_hir_pretty/src/lib.rs

@@ -1070,8 +1070,6 @@ impl<'a> State<'a> {
     ) {
         match blk.rules {
             hir::BlockCheckMode::UnsafeBlock(..) => self.word_space("unsafe"),
-            hir::BlockCheckMode::PushUnsafeBlock(..) => self.word_space("push_unsafe"),
-            hir::BlockCheckMode::PopUnsafeBlock(..) => self.word_space("pop_unsafe"),
             hir::BlockCheckMode::DefaultBlock => (),
         }
         self.maybe_print_comment(blk.span.lo());