Remove methods on `ClientBulder` that don't serve a purpose (#2953) #942

Job	Run time
Examples	2m 46s
Build docs	45s
Test (macOS)	1m 34s
Check minimal versions	47s
MSRV	0s
Test (nightly)	1m 58s
Test (stable)	3m 31s
Test (beta)	2m 58s
Test (Windows)	5m 27s
Test (native-tls)	2m 30s
Test (no default features)	56s
Test (no cache)	2m 22s
Test (no gateway)	1m 44s
Test (unstable Discord API features)	2m 37s
Test (chrono, chrono)	1m 17s
Test (unstable API + typesize, default unstable typesize, true)	1m 2s
Test (builder without model, builder, true)	40s
Test (unstable Discord API (no default features), unstable, true)	36s
	33m 30s

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