gnu: Use ‘define-deprecated-package’ for deprecated packages.

Use ‘define-deprecated-package’ instead of (define x (deprecated-package …))
throughout gnu/packages/*.scm.

Change-Id: I4e176da9ac660327489dab256ca4d12c4e78fe8d

gnu/packages/elm.scm

@@ -174,8 +174,8 @@ such as @command{elm make} and @command{elm repl}.")
     (license license:bsd-3)))
 
 ;; The 'elm' package used to be called 'elm-compiler'.
-(define-public elm-compiler
-  (deprecated-package "elm-compiler" elm))
+(define-deprecated-package elm-compiler
+  elm)
 
 (define-public elm-core
   (package