contract-security-non-existent-KT-address: use rpc (#2091)

[arvidj]

To test:

1. Start local, sandboxed Octez node with RPC endpoint http://127.0.0.1:18731.
2. Run TEZOS_RPC_MONDAYNET=http://127.0.0.1:18731 npm run "test:mondaynet-secret-key" "contract-security-non-existent-KT-address.spec.ts"
3. The test should work with this fix, and will fail without it as described in Integration test contract-multisig-set-and-remove-delegate.spec.ts hardcodes node RPC endpoint #2091

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[roxaneletourneau]

Thank you very much for the fix @arvidj !