Rollup merge of #64139 - Mark-Simulacrum:strip-legacy-proc-macro, r=petrochenkov

Migrate internal diagnostic registration to macro_rules

Review is best done commit-by-commit.

Fixes #64132.

src/libsyntax_ext/error_codes.rs

@@ -1,9 +1,8 @@
-use syntax::register_long_diagnostics;
-
 // Error messages for EXXXX errors.
-// Each message should start and end with a new line, and be wrapped to 80 characters.
-// In vim you can `:set tw=80` and use `gq` to wrap paragraphs. Use `:set tw=0` to disable.
-register_long_diagnostics! {
+// Each message should start and end with a new line, and be wrapped to 80
+// characters.  In vim you can `:set tw=80` and use `gq` to wrap paragraphs. Use
+// `:set tw=0` to disable.
+syntax::register_diagnostics! {
 E0660: r##"
 The argument to the `asm` macro is not well-formed.
 

src/libsyntax_ext/lib.rs

@@ -9,7 +9,6 @@
 #![feature(nll)]
 #![feature(proc_macro_internals)]
 #![feature(proc_macro_quote)]
-#![feature(rustc_diagnostic_macros)]
 
 extern crate proc_macro;