Remove PrepareStatementStateMachine #930

Job	Run time
gh-codeql	6m 59s
api-breakage	5m 14s
linux-unit (swift:5.6-focal)	2m 42s
linux-unit (swift:5.7-jammy)	2m 39s
linux-unit (swift:5.8-jammy)	2m 56s
linux-unit (swiftlang/swift:nightly-5.9-jammy)	4m 25s
linux-unit (swiftlang/swift:nightly-main-jammy)	4m 8s
linux-integration-and-dependencies (postgres:15)	7m 14s
linux-integration-and-dependencies (postgres:13)	6m 52s
linux-integration-and-dependencies (postgres:11)	8m 20s
macos-all (postgresql@14, scram-sha-256, ~14.3)	3m 7s
macos-all (postgresql@14, scram-sha-256, 15.0-beta)	4m 10s
	58m 46s

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