Remove redundant fields from Context #1136

Job	Run time
Build docs	1m 25s
Clippy	48s
Test (MSRV)	12s
Rustfmt	12s
Test (stable)	1m 57s
Test (beta)	1m 59s
Test (nightly)	1m 40s
Test (macOS)	2m 8s
Test (Windows)	3m 52s
Test (no features)	1m 10s
Test (all features - simdjson, cargo test --all-features --lib --tests --examples)	1m 15s
Test (native TLS, cargo test --all-features --features serenity/native_tls_backend --lib --tests ...	1m 22s
	18m 0s

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