Legacy function `getMessageByteSize` is overloaded and designed to handle now-deprecated encrypted msgs. It is also the last holdout still using the legacy `generateOpReturnScript`, which has been replaced by better functions in the `src/opreturn` directory.
Write a simpler function to get bytecount for Cashtab msgs. Add same unit tests as old function and some others.
Delete now unused functions `getMessageByteSize` and `generateOpReturnScript`.
Implement in Send.js