maintenance: Remove reference to removed populateCategory.php
Removed in 0dacf7d68d8d517cada731375f9612d8e060db58
Follow-Up: Id7fc111b71e8ee9a37a3e2e56849ac5afeea9f9d Change-Id: I6f317785e2698d16f9dc944ef0f0c6fff78e7229