Remove ir_ssa.rs as we aren't using it and it's now outdated

yjit/src/backend/mod.rs

@@ -5,5 +5,4 @@ pub mod x86_64;
 pub mod arm64;
 
 pub mod ir;
-pub mod ir_ssa;
 mod tests;

yjit/src/codegen.rs

@@ -1146,7 +1146,7 @@ fn gen_opt_plus(
         // Check that both operands are fixnums
         guard_two_fixnums(ctx, asm, side_exit);
 
-        // Get the operands and destination from the stack
+        // Get the operands from the stack
         let arg1 = ctx.stack_pop(1);
         let arg0 = ctx.stack_pop(1);