Base network displayed twice in network selector

### What is this about?

The Base network is displayed twice:
- once in the "Enabled networks" under the name `Base Mainnet`
- once under "Show test networks" under the name `Base Main Network`

### Scenario

_No response_

### Design

_No response_

### Technical Details

_No response_

### Threat Modeling Framework

_No response_

### Acceptance Criteria

Base is displayed once in the mainnet section, both in the network picker and the `Settings -> Networks` list

### Stakeholder review needed before the work gets merged

- [ ] Engineering (needed in most cases)
- [ ] Design
- [ ] Product
- [ ] QA (automation tests are required to pass before merging PRs but not all changes are covered by automation tests - please review if QA is needed beyond automation tests)
- [ ] Security
- [ ] Legal
- [ ] Marketing
- [ ] Management (please specify)
- [ ] Other (please specify)

### References

Introduced by https://github.com/MetaMask/metamask-mobile/pull/17409

Start by tracing the network picker and Settings -> Networks, then compare the network handling introduced by PR 17409. Verify the duplicate Base entries use the same identity and that the completed change displays Base only once in the mainnet section in both locations.

Written by the indexing model from the issue text.