Document no-longer emitted E0430/E0431

Author: mu001999

compiler/rustc_error_codes/src/error_codes/E0430.md

@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 The `self` import appears more than once in the list.
 
 Erroneous code example:
 
-```compile_fail,E0430
+```ignore (error is no longer emitted)
 use something::{self, self}; // error: `self` import can only appear once in
                              //        the list
 ```

compiler/rustc_error_codes/src/error_codes/E0431.md

@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 An invalid `self` import was made.
 
 Erroneous code example:
 
-```compile_fail,E0431
+```ignore (error is no longer emitted)
 use {self}; // error: `self` import can only appear in an import list with a
             //        non-empty prefix
 ```