Mob heads became dropped items instead of being cleared when replaced with air

Bug Description:
Mob heads drop as an item instead of being wiped out completely by replacing it with air using /fill or /setblock command or loading structure from structure block.

There's probably nothing wrong with it, but when your structure is full of mob heads and tried to clear the whole structure with structure block or /fill command, it can get annoying when you tried to clean all the mob heads dropped on the ground, because it can waste your time on structure building.

Steps to Reproduce:

1. Place a mob head
2. Replace the mob head with air by using the /setblock or /fill command

Observed Results:
The mob head drops as an item.

Expected Results:
The mob head should not drop as an item.