gnu: fillets-ng: Rename package to fish-fillets-ng.

* gnu/packages/games.scm (fillets-ng): Define in terms of
'deprecated-package'.
(fish-fillets-ng): New variable, formerly known as "fillets-ng".

gnu/packages/games.scm

@@ -4364,9 +4364,9 @@ shapes are arranged in a series of increasingly complex patterns, forming
  becoming difficult enough to tax even the brightest of minds.")
     (license license:gpl2+)))
 
-(define-public fillets-ng
+(define-public fish-fillets-ng
   (package
-    (name "fillets-ng")
+    (name "fish-fillets-ng")
     (version "1.0.1")
     (source (origin
               (method url-fetch)
@@ -4433,6 +4433,9 @@ underwater realm quarrel among themselves or comment on the efforts of your
 fish.  The whole game is accompanied by quiet, comforting music.")
     (license license:gpl2+)))
 
+(define-public fillets-ng
+  (deprecated-package "fillets-ng" fish-fillets-ng))
+
 (define-public crawl
   (package
     (name "crawl")