Change MessageUpdateEvent to just contain a full Message (#3061) #1066

# to view logs

Job	Run time
Examples	3m 18s
Build docs	58s
Check minimal versions	1m 0s
Test (macOS)	4m 4s
MSRV	0s
Test (nightly)	1m 54s
Test (stable)	2m 24s
Test (beta)	2m 40s
Test (Windows)	6m 50s
Test (native-tls)	2m 15s
Test (no default features)	1m 5s
Test (no cache)	2m 6s
Test (no gateway)	1m 41s
Test (unstable Discord API features)	2m 24s
Test (zlib compression)	2m 18s
Test (zstd compression)	2m 14s
Test (zlib and zstd compression)	2m 23s
Test (chrono, chrono)	1m 3s
Test (unstable API + typesize, default unstable typesize, true)	1m 16s
Test (builder without model, builder, true)	49s
Test (unstable Discord API (no default features), unstable, true)	47s
	43m 29s

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