Cranelift: Make Opcode represented as a u8 instead of u16 and remove vestigial conversion impls (#5042)

* Cranelift: Make `Opcode` represented as a `u8` instead of `u16`

* Cranelift: Remove unused conversion impls for `Opcode`

These are vestigial, left over from Peepmatic.

cranelift/codegen/src/ir/instructions.rs

@@ -7,9 +7,7 @@
 //! directory.
 
 use alloc::vec::Vec;
-use core::convert::{TryFrom, TryInto};
 use core::fmt::{self, Display, Formatter};
-use core::num::NonZeroU32;
 use core::ops::{Deref, DerefMut};
 use core::str::FromStr;
 
@@ -77,24 +75,6 @@ impl Opcode {
     }
 }
 
-impl TryFrom<NonZeroU32> for Opcode {
-    type Error = ();
-
-    #[inline]
-    fn try_from(x: NonZeroU32) -> Result<Self, ()> {
-        let x: u16 = x.get().try_into().map_err(|_| ())?;
-        Self::try_from(x)
-    }
-}
-
-impl From<Opcode> for NonZeroU32 {
-    #[inline]
-    fn from(op: Opcode) -> NonZeroU32 {
-        let x = op as u8;
-        NonZeroU32::new(x as u32).unwrap()
-    }
-}
-
 // This trait really belongs in cranelift-reader where it is used by the `.clif` file parser, but since
 // it critically depends on the `opcode_name()` function which is needed here anyway, it lives in
 // this module. This also saves us from running the build script twice to generate code for the two