Added @available derectives for MIDIMonitorKeyboard and removed Previ… #38

Job	Run time
Test / Create Swift Test Matrix	2s
Test / xcodebuild test (ios, swift 5.5)	4m 20s
Test / xcodebuild test (ios, swift 5.6)	4m 30s
Test / swift test (macos, swift 5.5)	1m 34s
Test / swift test (macos, swift 5.6)	1m 19s
Build KeyboardDemo (iOS) (Xcode 13.2)	1m 56s
Build KeyboardDemo (iOS) (Xcode 13.4)	1m 44s
Build KeyboardDemo (macOS) (Xcode 13.2)	4m 56s
Build KeyboardDemo (macOS) (Xcode 13.4)	1m 57s
Send Notification	0s
	22m 18s

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