Remove a few redundant `.hs-boot` files

There don't seem to be any corresponding `{-# SOURCE #-}` for the removed
`.hs-boot`-files anymore (if there ever was any in the first place).

This also removes a commented out `{-# SOURCE #-}` import which turns up when
grepping the source for `{-# SOURCE #-}` occurences.

libraries/base/Data/OldTypeable/Internal.hs-boot

-{-# LANGUAGE Unsafe #-}
-{-# LANGUAGE CPP, NoImplicitPrelude, MagicHash #-}
-
-module Data.OldTypeable.Internal (
-    Typeable(typeOf),
-    TypeRep,
-    TyCon,
-    mkTyCon,
-    mkTyConApp
-  ) where
-
-import GHC.Base
-
-data TypeRep
-data TyCon
-
-#include "MachDeps.h"
-
-#if WORD_SIZE_IN_BITS < 64
-mkTyCon :: Word64# -> Word64# -> String -> String -> String -> TyCon
-#else
-mkTyCon :: Word#   -> Word#   -> String -> String -> String -> TyCon
-#endif
-
-mkTyConApp   :: TyCon -> [TypeRep] -> TypeRep
-
-class Typeable a where
-  typeOf :: a -> TypeRep

libraries/base/Data/Typeable/Internal.hs-boot

-{-# LANGUAGE Unsafe #-}
-{-# LANGUAGE CPP, NoImplicitPrelude, MagicHash, PolyKinds #-}
-
-module Data.Typeable.Internal (
-    Proxy(..),
-    Typeable(typeRep),
-    TypeRep,
-    TyCon,
-    mkTyCon,
-    mkTyConApp
-  ) where
-
-import GHC.Base
-import {-# SOURCE #-} Data.Proxy
-
-data TypeRep
-data TyCon
-
-#include "MachDeps.h"
-
-#if WORD_SIZE_IN_BITS < 64
-mkTyCon :: Word64# -> Word64# -> String -> String -> String -> TyCon
-#else
-mkTyCon :: Word#   -> Word#   -> String -> String -> String -> TyCon
-#endif
-
-mkTyConApp   :: TyCon -> [TypeRep] -> TypeRep
-
-class Typeable a where
-  typeRep :: proxy a -> TypeRep

libraries/base/GHC/Show.lhs-boot

-\begin{code}
-{-# LANGUAGE Trustworthy #-}
-{-# LANGUAGE NoImplicitPrelude #-}
-
-module GHC.Show (showSignedInt) where
-
-import GHC.Types
-
-showSignedInt :: Int -> Int -> [Char] -> [Char]
-\end{code}
-

libraries/base/GHC/Word.hs

@@ -35,7 +35,6 @@ import Data.Maybe
 import GHC.IntWord64
 #endif
 
--- import {-# SOURCE #-} GHC.Exception
 import GHC.Base
 import GHC.Enum
 import GHC.Num