Remove feature that wasn't added

Author: Daniel Smith

crates/std_detect/src/detect/arch/x86.rs

@@ -74,7 +74,6 @@ features! {
     /// * `"avx512bitalg"`
     /// * `"avx512bf16"`
     /// * `"avx512vp2intersect"`
-    /// * `"knc"`
     /// * `"f16c"`
     /// * `"fma"`
     /// * `"bmi1"`