Rollup merge of #35648 - ahmedcharles:pred, r=alexcrichton

Predicates haven't existed in almost 5 years.

This test probably adds negative value other than historical amusement.

src/test/run-pass/pred-not-bool.rs

@@ -1,18 +0,0 @@
-// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-// this checks that a pred with a non-bool return
-// type is rejected, even if the pred is never used
-
-// pretty-expanded FIXME #23616
-
-fn bad(_a: isize) -> isize { return 37; } //~ ERROR Non-boolean return type
-
-pub fn main() { }