Remove expect-fx syntax and handling

This was never fully hooked up in platforms, and the plan is to replace the need for this with doing purity-inference on normal `expect` statements.

On the other hand, fuzzing is finding some bugs caused by having a hyphenated keyword, so this is a great time to go ahead and remove it!

crates/compiler/parse/src/normalize.rs

@@ -427,13 +427,6 @@ impl<'a> Normalize<'a> for ValueDef<'a> {
                 condition: arena.alloc(condition.normalize(arena)),
                 preceding_comment: Region::zero(),
             },
-            ExpectFx {
-                condition,
-                preceding_comment: _,
-            } => ExpectFx {
-                condition: arena.alloc(condition.normalize(arena)),
-                preceding_comment: Region::zero(),
-            },
             ModuleImport(module_import) => ModuleImport(module_import.normalize(arena)),
             IngestedFileImport(ingested_file_import) => {
                 IngestedFileImport(ingested_file_import.normalize(arena))