refactor(tvix/eval): remove redundant clone

This CL removes redundant clone from value which is
going to be dropped without further use.

Change-Id: Ibd2a724853c5cfbf8ca40bf0b3adf0fab89b9be5
Signed-off-by: Aaqa Ishtyaq <aaqaishtyaq@gmail.com>
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8125
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

tvix/eval/src/compiler/optimiser.rs

@@ -9,7 +9,7 @@ use ast::Expr;
 pub(super) fn optimise_expr(c: &mut Compiler, slot: LocalIdx, expr: ast::Expr) -> ast::Expr {
     match expr {
         Expr::BinOp(_) => optimise_bin_op(c, slot, expr),
-        _ => expr.to_owned(),
+        _ => expr,
     }
 }