Move deposit contract rules to its own Makefile

[jtraglia]

As part of a series of PRs to clean up the Makefile, this one moves rules associated with the deposit contract to its own Makefile in the solidity_deposit_contract directory. This part of the project has ossified. Also:

• I updated dependency versions so tests work now. There was a conflict with eth2spec dependency versions.
• I removed CI workflow tasks associated with the deposit contract. The tests were already disabled.