Remove remnants of the checked feature

The Cargo feature `checked` was added in d166a30 ("Overhaul tests")
and later removed in 5e0eca7 ("swap stable to be unstable, checked
is now debug_assertions"). However, there are a few remaining uses of
`feature = "checked"` that did not get removed. Clean these up here.

build.rs

@@ -8,18 +8,13 @@ fn main() {
     println!("cargo:rerun-if-changed=build.rs");
     println!("cargo:rustc-check-cfg=cfg(assert_no_panic)");
 
-    println!("cargo:rustc-check-cfg=cfg(feature, values(\"checked\"))");
-
-    #[allow(unexpected_cfgs)]
-    if !cfg!(feature = "checked") {
-        let lvl = env::var("OPT_LEVEL").unwrap();
-        if lvl != "0" && !cfg!(debug_assertions) {
-            println!("cargo:rustc-cfg=assert_no_panic");
-        } else if env::var("ENSURE_NO_PANIC").is_ok() {
-            // Give us a defensive way of ensureing that no-panic is checked  when we
-            // expect it to be.
-            panic!("`assert_no_panic `was not enabled");
-        }
+    let lvl = env::var("OPT_LEVEL").unwrap();
+    if lvl != "0" && !cfg!(debug_assertions) {
+        println!("cargo:rustc-cfg=assert_no_panic");
+    } else if env::var("ENSURE_NO_PANIC").is_ok() {
+        // Give us a defensive way of ensureing that no-panic is checked  when we
+        // expect it to be.
+        panic!("`assert_no_panic `was not enabled");
     }
 
     configure::emit_libm_config(&cfg);

crates/compiler-builtins-smoke-test/Cargo.toml

@@ -22,7 +22,6 @@ unexpected_cfgs = { level = "warn", check-cfg = [
   "cfg(arch_enabled)",
   "cfg(assert_no_panic)",
   "cfg(intrinsics_enabled)",
-  'cfg(feature, values("checked"))',
   'cfg(feature, values("force-soft-floats"))',
   'cfg(feature, values("unstable"))',
   'cfg(feature, values("unstable-intrinsics"))',

src/math/rem_pio2_large.rs

@@ -226,8 +226,9 @@ pub(crate) fn rem_pio2_large(x: &[f64], y: &mut [f64], e0: i32, prec: usize) ->
     let x1p24 = f64::from_bits(0x4170000000000000); // 0x1p24 === 2 ^ 24
     let x1p_24 = f64::from_bits(0x3e70000000000000); // 0x1p_24 === 2 ^ (-24)
 
-    #[cfg(all(target_pointer_width = "64", feature = "checked"))]
-    assert!(e0 <= 16360);
+    if cfg!(target_pointer_width = "64") {
+        debug_assert!(e0 <= 16360);
+    }
 
     let nx = x.len();