gnu: music21: Rename to python-music21.

* gnu/packages/music.scm (music21): Rename to ...
(python-music21): ... this.
(music21): New deprecated package pointing to python-music21.

Change-Id: If64ecacb4ab458b23ea1baaf7e4ff0683010a97f
Signed-off-by: jgart <jgart@dismail.de>

gnu/packages/music.scm

@@ -1586,9 +1586,9 @@ Guile.")
 scores.")
     (license (package-license lilypond))))
 
-(define-public music21
+(define-public python-music21
   (package
-    (name "music21")
+    (name "python-music21")
     (version "9.3.0")
     (source
      (origin
@@ -1624,6 +1624,8 @@ listeners answer questions about music quickly and simply.")
     ;; Software is dual-licensed.
     (license (list license:bsd-3 license:lgpl3+))))
 
+(define-deprecated-package music21 python-music21)
+
 (define-public stk
   (package
     (name "stk")