A bit of a judgment call, imo could go either way. I leaned this way as

1. This function is related to getAliasTargetOutput, which is in this file. I modeled this function on that function. Both functions should get the alias buffer in the same way, so it is useful to have them grouped. We are getting part of an OP_RETURN and then getting the bytecount of that part.

2. The old function in aliasUtils is actually calling a to-be-deprecated much weirder way of getting the bytecount function from utils/cashMethods.js. So, while the unit tests are the same as the old ones (although I added a few more cases), the logic is new + related to an existing opreturn function

3. The unit test structure is much better here and it was easier to add new unit tests. Ultimately all the Cashtab unit tests should be refactored to follow the vectors approach of the newer function groups (opreturn and transactions). So, this was an opportunity and chip away at some of that work gradually, in line with deprecating the old function.