gnu: Move the deprecated 'ghc-stylish-haskell' closer to its replacement.

Inheritance across modules can cause unbound variable errors because
of cyclic dependencies between the modules.

* gnu/packages/haskell-xyz.scm (ghc-stylish-haskell): Move from here ...
* gnu/packages/haskell-apps.scm (ghc-stylish-haskell): ... to here.

gnu/packages/haskell-apps.scm

@@ -777,3 +777,6 @@ Replace some ASCII sequences by their Unicode equivalent (turned off by
 default)
 @end itemize")
     (license license:bsd-3)))
+
+(define-public ghc-stylish-haskell
+  (deprecated-package "ghc-stylish-haskell" stylish-haskell))

gnu/packages/haskell-xyz.scm

@@ -11118,9 +11118,6 @@ functions for breaking or splitting on substrings and replacing all
 occurrences of a substring (the first in case of overlaps) with another.")
     (license license:bsd-3)))
 
-(define-public ghc-stylish-haskell
-  (deprecated-package "ghc-stylish-haskell" stylish-haskell))
-
 (define-public ghc-svg-builder
   (package
     (name "ghc-svg-builder")