Fix missed diff in FoodMetaData. Fixes BUKKIT-4704

**The Issue:**


IN 1.6.2, when Players are healed from having the appropriate hunger amount, they are supposed to take 3 exhaustion, as detailed in
https://github.com/Bukkit/mc-dev/blob/master/net/minecraft/server/FoodMetaData.java#L39

However, it seems this diff was missed in the CraftBukkit update, resulting in that penalty not being issued on healing, deviating from vanilla behavior.

**PR Breakdown:**
This PR adds the missing exhaustion penalty and restores vanilla behavior.  In order to preserve the functionality of Cancelling a healing event,  the CraftBukkit constructed heal(float, RegainReason)  was altered to return a Boolean for success as opposed to being a void method, this was done in order to allow for the exhaustion penalty to only be issued when the healing event is not cancelled.

Also in this PR:  Remove unused CraftBukkit import from nms.

**Ticket:**
https://bukkit.atlassian.net/browse/BUKKIT-4704