examples/block-ip: drop redundant `memory.h` include

Not used elsewhere in the repo.

examples/block-ip: show how to block IP addresses

- Show how CURLOPT_OPENSOCKETFUNCTION can be used to block IP addresses.

This is a new example that demonstrates IP blocking.

examples/block-ip: show how to block IP addresses

- Show how CURLOPT_OPENSOCKETFUNCTION can be used to block IP addresses.

This is a new example that demonstrates IP blocking.

Ref: https://github.com/curl/curl/discussions/15710#discussioncomment-11534877

Closes https://github.com/curl/curl/pull/15748

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