Drop atpanic wrapper function

The use of longjmp in lua makes dealing with lua exceptions difficult.
There doesn't seem to be a sensible way to handle those exceptions, so
the host program will exit with a panic either way. With that in mind,
the `atpanic` function doesn't seem very useful.

src/Foreign/Lua.hs

@@ -41,7 +41,6 @@ module Foreign.Lua
   , module Foreign.Lua.Types
   , module Foreign.Lua.Util
   -- * Lua API functions
-  , atpanic
   , call
   , checkstack
   , close

src/Foreign/Lua/Api.hs

@@ -56,13 +56,6 @@ import qualified Data.ByteString as B
 import qualified Data.ByteString.Unsafe as B
 import qualified Foreign.Storable as F
 
--- | Sets a new panic function and returns the old one (see
--- <https://www.lua.org/manual/5.3/manual.html#4.6 §4.6> and
--- <https://www.lua.org/manual/5.3/manual.html#lua_atpanic lua_atpanic> in the
--- lua manual).
-atpanic :: FunPtr LuaCFunction -> Lua (FunPtr LuaCFunction)
-atpanic = liftLua1 lua_atpanic
-
 -- | See <https://www.lua.org/manual/5.3/manual.html#lua_call lua_call>.
 call :: NumArgs -> NumResults -> Lua ()
 #if LUA_VERSION_NUMBER >= 502