Auto merge of #23156 - GuillaumeGomez:remove-proc, r=alexcrichton

This is the implementation of the [RFC 584](https://github.com/rust-lang/rfcs/pull/584).

src/test/parse-fail/obsolete-proc.rs

@@ -10,8 +10,8 @@
 
 // Test that we generate obsolete syntax errors around usages of `proc`.
 
-fn foo(p: proc()) { } //~ ERROR obsolete syntax: the `proc` type
+fn foo(p: proc()) { } //~ ERROR `proc` is a reserved keyword
 
-fn bar() { proc() 1; } //~ ERROR obsolete syntax: `proc` expression
+fn bar() { proc() 1; }
 
-fn main() { }
+fn main() { }