convert the optimize attribute to a new parser

compiler/rustc_error_codes/src/error_codes/E0722.md

@@ -1,8 +1,14 @@
+#### Note: this error code is no longer emitted by the compiler
+
+This is because it was too specific to the `optimize` attribute.
+Similar diagnostics occur for other attributes too.
+The example here will now emit `E0539`
+
 The `optimize` attribute was malformed.
 
 Erroneous code example:
 
-```compile_fail,E0722
+```compile_fail,E0539
 #![feature(optimize_attribute)]
 
 #[optimize(something)] // error: invalid argument