updated historical terms with modern equivalents

updated historical terms with modern equivalents

### Description
There were a few remnant uses of master/slave in the code and docs. The project previously made a decision to move away from them to use modern and inclusive terminology.

This PR does not cover a bug or necessitate a documented entry into the changelog, so an issue ticket was not created.

### Checklist
This pull request is:

- [x] A documentation / typographical error fix
- [x] A short code fix
- [ ] A new feature implementation

Closes: #5381
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/5381
Pull-request-sha: 92597e83d0e1e18960dbb39b604b313e7a1cbb30

Change-Id: I1fb34fe5ab6c19fd7360568d7b51cdea9d271b3b
(cherry picked from commit 3512d51600c250f72911313e3f204552c250ece7)