Remove reg_universe method from MachBackend and MachInst

cranelift/codegen/src/isa/aarch64/mod.rs

@@ -58,7 +58,7 @@ impl AArch64Backend {
     ) -> CodegenResult<VCode<inst::Inst>> {
         let emit_info = EmitInfo::new(flags.clone());
         let abi = Box::new(abi::AArch64ABICallee::new(func, flags)?);
-        compile::compile::<AArch64Backend>(func, self, abi, self.reg_universe(), emit_info)
+        compile::compile::<AArch64Backend>(func, self, abi, &self.reg_universe, emit_info)
     }
 }
 
@@ -110,10 +110,6 @@ impl MachBackend for AArch64Backend {
         self.isa_flags.iter().collect()
     }
 
-    fn reg_universe(&self) -> &RealRegUniverse {
-        &self.reg_universe
-    }
-
     fn unsigned_add_overflow_condition(&self) -> IntCC {
         // Unsigned `>=`; this corresponds to the carry flag set on aarch64, which happens on
         // overflow of an add.