Remove all mention of Smart Contracts, or Contracts

[segfaultxavi]

As per Discord discussion:

Smart contracts have become synonymous with the EVM and Turing-complete chains. Even calling them dumb contracts or any kind of amalgamation of contract is a bit disingenuous.

Now note - the case can be made that we have smart contracts according to Szabo’s definition. Bitcoin and Symbol both have multisig accounts, which are a type of smart contract. However, we still have the problem where the general public associates smart contracts with the EVM, and so unless we add a primer on Szabo’s paper and smart contracts as they exist on other chains (and what capabilities we do and don’t have) it might be best to omit.