Revert "Adopt h2handler multiplexer (#1587)" #850

Job	Run time
License Header and Formatting Checks	2m 22s
Integration Tests on swiftlang/swift:nightly-focal	4m 53s
Integration Tests on swift:5.8-jammy	2m 57s
Integration Tests on swift:5.7-jammy	3m 41s
Integration Tests on swift:5.6-focal	3m 31s
Build and Test on swiftlang/swift:nightly-focal	4m 56s
Build and Test on swift:5.8-jammy	4m 37s
Build and Test on swift:5.7-jammy	4m 25s
Build and Test on swift:5.6-focal	2m 42s
Performance Tests on swiftlang/swift:nightly-focal	12m 17s
Performance Tests on swift:5.8-jammy	9m 11s
Performance Tests on swift:5.7-jammy	9m 3s
Performance Tests on swift:5.6-focal	9m 15s
	1h 13m 50s

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