soroban-rpc: Remove deprecated getContractData method

Deprecated in favour of getLedgerEntry. To be removed in the next release.

- [x] soroban-rpc: https://github.com/stellar/soroban-tools/pull/345
- [x] js-soroban-client: https://github.com/stellar/js-soroban-client/pull/40
- [x] ~soroban-cli?~
- [x] docs
  - waiting on https://github.com/stellar/soroban-docs/pull/253