Remove the use of ptree dependency

[abizjak]

Description

The ptree dependency has not been updated for some time, and in particular it depends on nom version 5, which uses Rust features that will be deprecated

> warning: trailing semicolon in macro used in expression position
>    --> /home/abizjak/.cargo/registry/src/github.com-1ecc6299db9ec823/nom-5.1.2/src/combinator/macros.rs:509:35
>     |
> 509 |     map!(__impl $i, call!($f), $g);
>     |                                   ^
>     |
>    ::: /home/abizjak/.cargo/registry/src/github.com-1ecc6299db9ec823/nom-5.1.2/src/number/complete.rs:595:3
>     |
> 595 |   map!(i, le_u128, |x| x as i128)
>     |   ------------------------------- in this macro invocation
>     |
>     = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
>     = note: for more information, see issue #79813 <https://github.com/rust-lang/rust/issues/79813>
>     = note: macro invocations at the end of a block are treated as expressions
>     = note: to ignore the value produced by the macro, add a semicolon after the invocation of `map`
>     = note: `#[allow(semicolon_in_expressions_from_macros)]` on by default
>     = note: this warning originates in the macro `map` (in Nightly builds, run with -Z macro-backtrace for more info)

We use this for pretty printing the contract state as a key-value store. However that is not really useful for users since it is too complex.

We should either replace the use of ptree, or remove this state printing feature.