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/load_internal/src/docs.rs

@@ -273,9 +273,6 @@ fn generate_entry_docs(
                     // Don't generate docs for `expect`s
                 }
 
-                ValueDef::ExpectFx { .. } => {
-                    // Don't generate docs for `expect-fx`s
-                }
                 ValueDef::ModuleImport { .. } => {
                     // Don't generate docs for module imports
                 }