Switch construct_runtime! to use default syntax

[bkchr]

Currently we are still declaring for every pallet all the parts we want to use for it:

runtimes/relay/polkadot/src/lib.rs

Line 1437 in d67b905

Babe: pallet_babe::{Pallet, Call, Storage, Config<T>, ValidateUnsigned} = 2,

Instead we can just write:

Babe: pallet_babe = 2,

There is no real reason to continue using the old syntax of always declaring all parts and it is also more error prone.

[Aideepakchaudhary]

@bkchr I think this issue is solved here: #152

[bkchr]

Yes! thank you