Revert "[FEATURE] improve memo support"

This reverts commit 89adcf4f4eebe1a5cc92a1b24b53f637422b96da.
[TASK] bump ripple-lib to 0.9.4-rc2
[DOC] update release notes
[TASK] bump version to 0.9.4
[TASK] update sjcl

- native support for k256
- improved entropy by taking advantage of platform crypto

- remove unnecessary sjcl overrides from sjcl-secp256k1.js
- updated ripple-lib curve instantiations to use k256
- add curve override so c256 points to k256

https://github.com/bitwiseshiftleft/sjcl/commit/16dde36fa2a58845f639429acd5bc4e4ebb5a0f1
Merge pull request #220 from geertweening/update_sjcl

[TASK] update sjcl
Cleanup

- Deprecate 'save' event
- Add TransactionQueue.getMinLedger(), use this as ledger_index_min
  in account_tx request on reconnect
- tx.sign() no longer accepts a callback
- Add various setters and jsdoc to transaction.js
- Normalize setters, e.g. sourceTag() and destinationTag()
- Minor optimization in call to tx.hash() in TransactionManager prior
  to submit; allow `serialized` argument to tx.hash() such that the
  transaction is not serialized twice
Make LastLedgerSequence offset configurable, default to 3
Do not bump LastLedgerSequence on resubmit
Rework tef and tel-class transaction error handling

Do not finalize tef or tel-class errors until LastLedgerSequence is
exceeded. Transactions that fail in this way will now be aborted
with a tej-class error. Errors like tefALREADY and tefMAX_LEDGER
should now be opaque to the user and have no consequence in
determining a final state.