message: Remove default derive for MemoryExtra
diff: @@ -6,7 +6,7 @@ use rustc_target::abi::Size;
  use crate::{stacked_borrows, intptrcast};
  use crate::stacked_borrows::Tag;
  -#[derive(Default, Clone, Debug)]
  +#[derive(Clone, Debug)]
  pub struct MemoryExtra {
  pub stacked_borrows: stacked_borrows::MemoryExtra,
  pub intptrcast: intptrcast::MemoryExtra,
  