added TODO in PlantType.java and made variables private in CustomPlantTypeTest

src/main/java/net/minecraftforge/common/PlantType.java

@@ -22,6 +22,7 @@ package net.minecraftforge.common;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.IWorldReader;
 
+// TODO 1.16: This should not be an enum. Change it to ToolType instead
 public enum PlantType implements IExtensibleEnum
 {
     Plains,