X.L.TrackFloating: Drop redundant _wasFloating

It was added in 81d338952d in an attempt to fix focus handling after
closing a floating window, but shortly after made redundant in
a551d1367c when we noticed it causes more harm than good. Unfortunately
it wasn't fully reverted, making the code more complex than necessary.

Drop the remaining bits.

Now it's almost obvious that the only difference between this and
X.L.StateFull.FocusTracking is the isF condition.

BTW the original issue 81d338952d was trying to fix can be fixed by
using X.H.RefocusLast, from the author of X.L.StateFull.FocusTracking.
:-)

XMonad/Layout/TrackFloating.hs

@@ -47,14 +47,12 @@ import qualified XMonad.StackSet as W
 import qualified Data.Traversable as T
 
 
-data TrackFloating a = TrackFloating
-    { _wasFloating :: Bool,
-      _tiledFocus :: Maybe Window }
-    deriving (Read,Show,Eq)
+data TrackFloating a = TrackFloating (Maybe Window)
+    deriving (Read,Show)
 
 
 instance LayoutModifier TrackFloating Window where
-    modifyLayoutWithUpdate os@(TrackFloating _wasF mw) ws@(W.Workspace{ W.stack = ms }) r
+    modifyLayoutWithUpdate (TrackFloating mw) ws@(W.Workspace{ W.stack = ms }) r
       = do
         winset <- gets windowset
         let xCur = fmap W.focus xStack
@@ -71,9 +69,7 @@ instance LayoutModifier TrackFloating Window where
             newState | isF = mw
                      | otherwise = xCur
         ran <- runLayout ws{ W.stack = newStack } r
-        return (ran,
-                let n = TrackFloating isF newState
-                in guard (n /= os) >> Just n)
+        return (ran, guard (newState /= mw) >> Just (TrackFloating newState))
 
 
 
@@ -142,7 +138,7 @@ window regardless of which tiled window was focused before.
 
 -}
 trackFloating ::  l a -> ModifiedLayout TrackFloating l a
-trackFloating layout = ModifiedLayout (TrackFloating False Nothing) layout
+trackFloating layout = ModifiedLayout (TrackFloating Nothing) layout
 
 {- $layoutModifier
 It also corrects focus issues for full-like layouts inside other layout