Remove rpc endpoint deprecated in v1.18 #6578

Job	Run time
cargo-test-sbf (token/program)	10m 18s
check	4m 16s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	14m 22s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	10m 37s
cargo-test-sbf (token-upgrade/program)	8m 38s
test (token/cli, token/program, token/program-2022, associated-token-account/program, instruction...	18m 47s
cargo-test-sbf (feature-proposal/program)	8m 18s
test (single-pool/cli, single-pool/program)	19m 11s
cargo-test-sbf (governance/addin-mock/program, governance/program)	11m 54s
test (token-upgrade/cli, token-upgrade/program)	12m 37s
cargo-test-sbf (memo/program)	8m 48s
cargo-test-sbf (name-service/program)	8m 58s
cargo-test-sbf (stake-pool/program)	12m 10s
cargo-test-sbf (single-pool/program)	9m 42s
	2h 38m 36s

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