Remove keccak256 crate and migrate keccak plain to eth-types (privacy…

…-scaling-explorations#1440)

### Description

- We remove the keccak256 crate.
- We migrate the keccak256 plain implementation to the eth-types crate.

As we migrate keccak circuit to the zkevm-crate, most of the functions
left in keccak256 crate are unused except of the plain keccak hash
implementation.

Most of the crates in the codebase depend on keccak256 crate because
they use the plain keccak hash. The plain keccak hash is only 300 lines
big. It would be beneficial to keep a plain implementation for people to
audit the optimized keccak circuit.

### Type of change

Bug fix (non-breaking change which fixes an issue)

.github/labeler.yml

@@ -16,8 +16,6 @@ crate-geth-utils:
   - geth-utils/**/*
 crate-integration-tests:
   - integration-tests/**/*
-crate-keccak:
-  - keccak256/**/*
 crate-mock:
   - mock/**/*
 crate-prover: