Fix fake import in GHC.Exception.Type boot module

It seems like I imported "GHC.Types ()" thinking that it would
transitively import GHC.Num.Integer when I wrote that module; but it
doesn't.

This led to build failures.
See https://mail.haskell.org/pipermail/ghc-devs/2021-March/019641.html

libraries/base/GHC/Base.hs

@@ -147,35 +147,37 @@ default ()              -- Double isn't available yet
 Note [Depend on GHC.Num.Integer]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-The Integer type is special because GHC.Iface.Tidy uses constructors in
-GHC.Num.Integer to construct Integer literal values. Currently it reads the
-interface file whether or not the current module *has* any Integer literals, so
-it's important that GHC.Num.Integer is compiled before any other module.
-
-(There's a hack in GHC to disable this for packages ghc-prim and ghc-bignum
-which aren't allowed to contain any Integer literals.)
-
-Likewise we implicitly need Integer when deriving things like Eq instances.
-
-The danger is that if the build system doesn't know about the dependency
-on Integer, it'll compile some base module before GHC.Num.Integer,
+The Integer type is special because GHC.CoreToStg.Prep.mkConvertNumLiteral
+lookups names in ghc-bignum interfaces to construct Integer literal values.
+Currently it reads the interface file whether or not the current module *has*
+any Integer literals, so it's important that GHC.Num.Integer is compiled before
+any other module.
+
+The danger is that if the build system doesn't know about the implicit
+dependency on Integer, it'll compile some base module before GHC.Num.Integer,
 resulting in:
   Failed to load interface for ‘GHC.Num.Integer’
     There are files missing in the ‘ghc-bignum’ package,
 
-Bottom line: we make GHC.Base depend on GHC.Num.Integer; and everything
-else either depends on GHC.Base, or does not have NoImplicitPrelude
-(and hence depends on Prelude).
-
-Note: this is only a problem with the make-based build system. Hadrian doesn't
-seem to interleave compilation of modules from separate packages and respects
+Note that this is only a problem with the make-based build system. Hadrian
+doesn't interleave compilation of modules from separate packages and respects
 the dependency between `base` and `ghc-bignum`.
 
+To ensure that GHC.Num.Integer is there, we must ensure that there is a visible
+dependency on GHC.Num.Integer from every module in base.  We make GHC.Base
+depend on GHC.Num.Integer; and everything else either depends on GHC.Base,
+directly on GHC.Num.Integer, or does not have NoImplicitPrelude (and hence
+depends on Prelude).
+
+The lookup is only disabled for packages ghc-prim and ghc-bignum, which aren't
+allowed to contain any Integer literal.
+
+
 Note [Depend on GHC.Tuple]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 Similarly, tuple syntax (or ()) creates an implicit dependency on
 GHC.Tuple, so we use the same rule as for Integer --- see Note [Depend on
-GHC.Integer] --- to explain this to the build system.  We make GHC.Base
+GHC.Num.Integer] --- to explain this to the build system.  We make GHC.Base
 depend on GHC.Tuple, and everything else depends on GHC.Base or Prelude.
 
 -}

libraries/base/GHC/Err.hs

@@ -26,7 +26,6 @@ module GHC.Err( absentErr, error, errorWithoutStackTrace, undefined ) where
 import GHC.Types (Char, RuntimeRep)
 import GHC.Stack.Types
 import GHC.Prim
-import GHC.Num.Integer ()   -- See Note [Depend on GHC.Num.Integer] in GHC.Base
 import {-# SOURCE #-} GHC.Exception
   ( errorCallWithCallStackException
   , errorCallException )

libraries/base/GHC/Exception/Type.hs-boot

@@ -9,7 +9,7 @@ module GHC.Exception.Type
   , underflowException
   ) where
 
-import GHC.Types ()
+import GHC.Num.Integer ()   -- See Note [Depend on GHC.Num.Integer] in GHC.Base
 
 data SomeException
 divZeroException, overflowException,

libraries/base/GHC/IO.hs-boot

@@ -4,7 +4,6 @@
 module GHC.IO where
 
 import GHC.Types
-import GHC.Num.Integer () -- See Note [Depend on GHC.Num.Integer] in GHC.Base
 import {-# SOURCE #-} GHC.Exception.Type (SomeException)
 
 mplusIO :: IO a -> IO a -> IO a

libraries/base/Unsafe/Coerce.hs

@@ -21,7 +21,6 @@ module Unsafe.Coerce
 
 import GHC.Arr (amap) -- For amap/unsafeCoerce rule
 import GHC.Base
-import GHC.Num.Integer () -- See Note [Depend on GHC.Num.Integer] in GHC.Base
 
 import GHC.Types