Remove `max_block_size` limit/parameter

**Task description**

`max_block_size` was introduced originally as a way to limit block size to prevent problems.

As it stands now the block energy limit implies a block size limit, modulo update instructions, and it would simplify the code to remove it.

If update keys are compromised then the chain has other problems than energy limit, so removing that does not seem to pose additional risks.

The issue names no files, tests, or entry points. Start by searching the repository for max_block_size and tracing its use alongside the block energy limit; done means the parameter and limit are removed consistently without leaving affected references or failing tests.

Written by the indexing model from the issue text.