docs: Local Evaluation and Edge Proxy 'pros, cons and caveats' no longer exist

[matthewelwell]

The documentation that existed here which outlined the pros, cons and caveats of local evaluation mode (and Edge Proxy) seems to have been lost in the documentation revamp.

We need to review all links (and any redirects) that currently end up at integrating-with-flagsmith/integration-overview since this seems to be the sink that has taken the traffic that used to be pointed to the previous documentation.

Some key examples that need to be updated:

• https://docs.flagsmith.com/integrating-with-flagsmith/sdks/server-side#local-evaluation-mode-network-behaviour
• https://docs.flagsmith.com/performance/edge-proxy#how-does-it-work