[MC-199151] Some blocks in savanna_large_farm_1 have grass blocks beneath them

The bug

In the structure minecraft:village/savanna/houses/savanna_large_farm_1, grass blocks are randomly present beneath the farm. This occurs beneath:

Every water source block
Every acacia stair
Every composter

In the screenshot below, every brown mushroom block represents dirt, every green wool represents a grass block that is out of place, and every lime wool represents a grass block that seems to be in the correct place.

How to reproduce

Give yourself a structure block using the command /give @p structure_block
Set the random tick speed to 0 to ensure that the blocks do not change using the command /gamerule randomTickSpeed 0
Place the structure block, and set it to Load mode
Paste the following into the structure block's "Structure Name" field:
```
minecraft:village/savanna/houses/savanna_large_farm_1
```

Prepare the position and then load the structure into your world
Use the F3 debug menu to see what type of block you are looking at