Remove `plutus-core` dependencies from `plutus-ledger-api`, `plutus-tx`.

`plutus-core` is difficult to build due to its c library dependencies which makes `plutus-ledger-core` and `plutus-tx` also difficult to build as they currently require `plutus-core`. By removing `plutus-core` dependency from `plutus-ledger-api` and `plutus-tx` we can potentially build them without using nix which is a big win for user experience.

This is also more "correct" to have `plutus-tx` and `plutus-ledger-api` completely abstracted from `plutus-core` since former is user-facing interface and latter is internal implementation that user is unlikely to interact with. This is similar to how Aiken did it: Aiken have their standard library completely isolated from their UPLC definitions and CEK implementation.