Remove help commands from built-ins #1194

Job	Run time
Test (MSRV)	1m 25s
Clippy	1m 14s
Test (stable)	2m 23s
Build docs	1m 25s
Rustfmt	8s
Test (beta)	2m 4s
Test (nightly)	1m 45s
Test (macOS)	1m 39s
Test (Windows)	4m 51s
Test (no features)	1m 10s
Test (all features - simdjson, cargo test --all-features --lib --tests --examples)	1m 10s
Test (native TLS, cargo test --all-features --features serenity/native_tls_backend --lib --tests ...	1m 24s
	20m 38s

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