use mainnet-geth, and not mainnet-light-geth for public swarm nodes

[nonsense]

light geth nodes are not as stable as fast synced geth nodes.

we are getting no suitable peers errors often on swarm-gateways.net , due to us using light geth nodes.

we should switch to fast synced regular geth nodes.

[nonsense]

We decided to use Cloudflare for the time being, in order to focus on Swarm and operating Swarm, rather than Geth. Geth works fine on on-demand instances, but most of our envs are composed of spot instances, and this is rather tricky to operate for a zero-downtime setting.