API Remove deprecation notice from method we're not removing

[GuySartorelli]

We can't remove this method, because it will still be inherited from SingleSelectField.

If the empty string has been set, it is used by getPlaceholder() - so I think just keeping the method with no deprecation is ultimately fine. We prefer people to use setPlaceholder() but if they use setEmptyString() instead it'll be handled appropriately.

Issue

• Remove deprecated code .github#311

[emteknetnz]

There's a probably a good reason to not call setEmptyString in SearchableDropdownField. I think it would make sense to keep the deprecation and upgrade it to throwing an exception in CMS 6 rather the removing the method.

[GuySartorelli]

What is the good reason to not call that method? It's explicitly handled in getPlaceholder(). The only reason this deprecation warning is here is because I asked for it, though I think I was wrong to do so.