Don't build the chain information of parachains

[tomaka]

The light client currently builds the chain information of parachains.
This is a very CPU-heavy operation, and all the chain information is used for is determine the genesis runtime hash.

[tomaka]

This turns out to not really be possible. Calculating the genesis hash requires knowing the state trie root, which in turn requires extracting the state version from the runtime.

Opened #1017 instead.

[tomaka]

Calculating the genesis hash requires knowing the state trie root, which in turn requires extracting the state version from the runtime.

I don't know what was in my mind, but the state trie root can be found directly in the chain spec, that was actually the entire point of the issue.

Reopening.