check-each-crate: Do not reference crate to check by name (#2098)

This pull request changes how `check-each-crate.py` is working. Instead
of passing the name of the crate via `-p`, we now jump into the
directory of the crate and call there `cargo check`. This should fix
issues like https://github.com/paritytech/polkadot-sdk/issues/2013 where
a crate is present twice in the `Cargo.lock`.

Besides that it also changes `core/Cargo.toml` to not always pull in
bandersnatch.