Clean up some old .md files #6028

Job	Run time
build-and-check	3m 13s
test-integration-packages/billing	1m 7s
test-integration-packages/internal	1m 14s
test-integration-common	44s
test-integration-sdk	1m 35s
test-integration-web	42s
test-integration-packages/agent-runtime	43s
test-integration-cli	44s
test-common	44s
test-.agents	42s
test-packages/internal	49s
test-packages/billing	42s
test-web	51s
test-sdk	46s
test-packages/agent-runtime	1m 12s
test-cli	52s
	16m 40s

Provide feedback