feat(binding-coap): remove cov:observe subprotocol #2622

Job	Run time
Tests (macos-latest, Node 18.x)	3m 29s
eslint	1m 22s
Tests (macos-latest, Node 20.x)	3m 28s
Check version consistency of packages	7s
Check coding style	11s
Tests (macos-latest, Node 22.x)	3m 40s
Tests (ubuntu-latest, Node 18.x)	2m 2s
Tests (ubuntu-latest, Node 20.x)	1m 53s
Tests (ubuntu-latest, Node 22.x)	2m 45s
Tests (windows-latest, Node 18.x)	5m 29s
Tests (windows-latest, Node 20.x)	5m 21s
Tests (windows-latest, Node 22.x)	5m 6s
	34m 53s

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