monster_metropolice is the original classname for the Metropolice in Half-Life 2. This entity shows up in the very earliest City 17 maps present in the WC Map pack.
Since we have no images of metropolice in-game from this era in development, the behavior and appearance of this entity is up for debate. It is very likely that this entity was used for the "trench cop" design shown on the Metropolice_(Evolution) page.
Mitigation / Entity Migration
In most cases, simply changing the classname of a monster_metropolice to npc_metropolice will work fine without any additional changes required.