revert __format__

CHANGELOG.md

@@ -33,12 +33,6 @@
   -  `freeze`  -> Use `ft.partial(tree_mask, lambda _: True)` instead.
   -  `unfreeze` -> Use `tree_unmask` instead.
 
--  Implement `__format__` for `TreeClass` for shorter syntax representation:
-   -  `f"{tree:3r}"` is tree **r**epr of depth = 3
-   -  `f"{tree:3s}"` is tree **s**tr of depth = 3
-   - `f"{tree:3d}"` is tree **d**iagram of depth = 3
-   -  `f"{tree:3t}`" is tree summary of depth = 3
-
 - `tree_{mask,unmask}` now accepts only callable `cond` argument.
 - Rename `is_frozen` to `is_masked`
   - frozen could mean non-trainable array, however the masking is not only for arrays but also for other types that will be hidden from jax transformations.