chore: remove agents/LESSONS.md #5639

Job	Run time
build-and-check	2m 43s
test-integration-packages/billing	1m 19s
test-integration-packages/internal	1m 5s
test-integration-sdk	41s
test-integration-packages/agent-runtime	41s
test-integration-common	39s
test-integration-web	41s
test-integration-cli	47s
test-packages/billing	40s
test-.agents	38s
test-cli	53s
test-packages/agent-runtime	52s
test-sdk	42s
test-web	56s
test-packages/internal	48s
test-common	39s
	14m 44s

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