Remove `ThinClient` from `dos/` #445

Job	Run time
check	0s
cargo-test-sbf (token/program)	8m 20s
test	0s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	12m 26s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	8m 40s
cargo-test-sbf (token-upgrade/program)	8m 48s
cargo-test-sbf (feature-proposal/program)	8m 43s
cargo-test-sbf (governance/addin-mock/program, governance/program)	11m 2s
cargo-test-sbf (memo/program)	7m 22s
cargo-test-sbf (name-service/program)	6m 29s
cargo-test-sbf (stake-pool/program)	11m 33s
cargo-test-sbf (single-pool/program)	9m 4s
	1h 32m 27s

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