Drop all plain HTTP snippets in favor of curl commands

[steve-chavez]

Problem

It's easy to forget adding both curl and HTTP syntax snippets. See: #719

Solution

Drop all existing HTTP snippets. Focus on only making the curl snippets readable from now on.

[laurenceisla]

Yes, I agree. I guess curl snippets are more useful for practical purposes than the HTTP ones. Also a consistent format should be kept for the snippets (could help if we want to add other snippets in the future).