Evaluate legacy 1559 functions

### Describe the bug

At present, we have a number of EIP1559-related functions in the codebase. Based on this comment (https://github.com/MetaMask/metamask-extension/pull/18064#discussion_r1144927433), we should consider looking at all functions that reference 1559 to see if they're actually necessary.

### Steps to reproduce

N/A

### Error messages or log output

_No response_

### Version

10.25

### Build type

None

### Browser

Chrome

### Operating system

Windows, MacOS

### Hardware wallet

_No response_

### Additional context

_No response_

Search the codebase for functions and references to 1559, then read the linked pull request discussion for the original context. Review each reference to determine whether it is still necessary; the work is complete when the legacy functions have been evaluated and the resulting cleanup or decision is clear.

Written by the indexing model from the issue text.