Why should it not be?
I agree that if it were the *primary* reason for such a change then it's a bit off, because the first concern for police officers should be safety. But if that's not compromised in any way, isn't it generally beneficial to ensure that the recruitment pool for Police Officers is as large as possible? Something that discourages, or could discourage, a subsection of the population from ever wanting to apply is something worth ditching if it's simply an "optional extra".
As to whether or not it will be effective in increasing recruitment among trans* people, who can say? But if it does, then I'd regard that as a benefit; and, if it does not, then no harm done.