Remove unused claude oauth #6367

Job	Run time
build-and-check	2m 47s
test-integration-packages/billing	1m 1s
test-integration-packages/internal	1m 14s
test-integration-common	46s
test-integration-cli	46s
test-integration-sdk	1m 19s
test-integration-web	39s
test-integration-packages/agent-runtime	42s
test-packages/agent-runtime	48s
test-.agents	51s
test-packages/internal	59s
test-packages/billing	51s
test-web	1m 11s
test-sdk	54s
test-cli	53s
test-common	43s
	16m 24s

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