There has been no official announcement from Princess about doing away with butlers in suite accommodations, so I have no idea where your travel agent got this piece of information. In my experience, some travel agents are better informed than others -- and there are quite a few travel agents who will spread any convenient rumor if they think that it might sway a customer to book on another line which has a lucrative promotion.
I personally don't believe anything that a travel agent tells me regarding possible changes in service until I have confirmation of it from a trustworthy source.
I'm somewhat confused about Princess's butler service. When it first started, it seemed to be only on ships that sailed in Europe for part of the year. I don't know whether it was an experimental program that didn't work out as expected (in which case it does make sense that it would be dropped) or if it's being extended fleet-wide. It's possible that your agent was misinformed about the extent of the program and incorrectly assumed that Princess was dropping it when a client took a cruise on a ship to which it had not been extended and reported back that it didn't happen.
In any case, other premium lines such as Celebrity have added butler service to their suite accommodations. From a competitive prespective, it does not make sense for Princess to drop it unless the other premium lines are doing likewise.