don't use .into() to convert types to identical types (clippy::useless_conversion)

Example:
let _x: String = String::from("hello world").into();

compiler/rustc_mir/src/transform/simplify_comparison_integral.rs

@@ -211,7 +211,7 @@ fn find_branch_value_info<'tcx>(
                 return None;
             };
             let branch_value_scalar = branch_value.literal.try_to_scalar()?;
-            Some((branch_value_scalar.into(), branch_value_ty, *to_switch_on))
+            Some((branch_value_scalar, branch_value_ty, *to_switch_on))
         }
         _ => None,
     }