Update "eth" to latest version from
https://github.com/ethereum/cpp-ethereum

This new version makes use of secp256k1 instead of custom
code and cryptopp to handle EC generation, and reduces its dependency
to boost to use more of the C++11 STL.

This allows to trim the code to completely remove the boost and
cryptopp dependencies.

Change-Id: I19118d3b833a9425cddbeabf6d0b6e07d5a4b15e