Understandably removed:
- Structure Blocks
- Command Blocks
Bare features:
- Death Messages
- Dropping Items
- Bee hives
- Most vanilla commands (/summon, /advancement, /attribute, /locatebiome, /locate, /spawnpoint, /gamemode, /seed, ...)
- Spawn eggs
- Spawners
- Gravity
- Bonemeal
- F3+F4 shortcut
- Dragon Eggs Teleporting
- Signed Books
Technical (but still vanilla):
- Negative attributes
- Negative colors
This list may be incomplete, feel free to suggest more bellow.