Completely remove old (non-segwit) transaction support

## Problem description

The code of BGL core is derived from Bitcoin core with some changes. The BTC is switching gradually to segwit transactions, while allowing older txs and addresses to still work. In BGL, those legacy transactions are not required.
In other words, remove support for P2PK[H] to be sure no 'old' transaction can be made, and leave only SegWit transactions supported.

## Solution direction
- carefully check in source code where transaction types are detected or formed;
- remove support for legacy transaction types where applicable;
- tread lightly, don't remove something if unsure;

## Acceptance criteria
- Old transaction types cannot be created though CLI/wallet, validated, etc.

Start by tracing where legacy transaction types are detected or formed across the CLI, wallet, and validation paths. Confirm that P2PK[H] transactions cannot be created or accepted, while SegWit transactions continue to work; the issue provides no specific files or tests to begin with.

Written by the indexing model from the issue text.