[Bug]: Privacy: Cannot remove some networks.

### Describe the bug

I am extremely privacy conscious and I want to be very sure that MetaMask isn't sending my information anywhere that I don't explicitly want it to. I have my own RPC node for the network I use and have configured MetaMask to use that. However, I cannot remove some networks (Linea, Ethereum, Testnets), and as a user I am concerned that MetaMask may be querying them in the background, at their default RPC endpoints.

I cannot change the default address with supplying an alternative, and I do not have an RPC node for some of these networks that I can configure because I do not use some of these networks.

### Expected behavior

I can disable features that I don't use, especially features that make external requests.

### Screenshots/Recordings

N/A

### Steps to reproduce

Go to settings > Networks and notice that there are a bunch of testnets and 3 mainnet networks that cannot be removed.

### Error messages or log output

```shell
N/A
```

### Detection stage

In production

### Version

7.51..0

### Build type

None

### Device

Pixel

### Operating system

Android

### Additional context

Even if these networks are not making queries in the background on their own, it would give me (user) a lot of peace of mind to be able to explicitly disable/remove them. I have no intention of using them, and I can always re-add them if I want to.

An alternative would be to allow me to disable these networks, if not remove them.

### Severity

Potential privacy issue, if actual background requests are being made then severe, if not then this should still be addressed in an abundance of caution and to make it clear to users that their privacy is being respected.

Start at Settings > Networks, the entry point described in the report, and trace how Linea, Ethereum, and testnets are presented compared with removable networks. Done means users can remove or explicitly disable unused networks and the behavior is verified for the listed networks, including the privacy concern about external requests.

Written by the indexing model from the issue text.