Fix: Incorrect event topic for chat message deletion

[coderabbitai[bot]]

The event topic in deleteChatMessage resolver uses ':chat_messages::create' for deletion operations, which is incorrect and could cause confusion for subscribers.

Current Behavior

The current implementation publishes deletion events with topic 'chats.[chatId]:chat_messages::create'

Expected Behavior

Deletion events should use topic 'chats.[chatId]:chat_messages::delete' to accurately reflect the operation type.

Context

• Found during review of PR #3201
• Comment link: https://github.com/PalisadoesFoundation/talawa-api/pull/3201#discussion_r1953335178

This should be addressed in a separate PR focused on server-side improvements.