Remove network beta support for Optimism from the supported-networks page

[p-diogo]

According to https://thegraph.com/docs/en/developing/supported-networks/ there's beta network support for Optimism. This is not true. It was a MIPs chain, but we didn't go through the process of activating it on mainnet while the program was active.

I tried updating docs myself, but it seems the source of truth for this table comes from an edgeandnode library:
https://github.com/edgeandnode/common/blob/ab0edee67fc012941d5a7169323c4dc1b6dcb3ed/src/constants/network.ts#L138

I don't want to risk messing it up. Can anyone else take over, please?