Clean up plan mode docs #5121

Job	Run time
build-and-check	2m 25s
test-cli	1m 15s
test-packages/billing	41s
test-packages/internal	36s
test-integration-.agents	1m 11s
test-npm-app	39s
test-common	47s
test-web	44s
test-sdk	55s
test-packages/agent-runtime	50s
test-integration-packages/billing	39s
test-backend	46s
test-integration-backend	46s
test-integration-packages/agent-runtime	46s
test-integration-cli	41s
test-integration-common	44s
test-integration-npm-app	42s
test-.agents	46s
test-integration-packages/internal	47s
test-integration-sdk	58s
test-integration-web	40s
	18m 18s

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