gnu: beets: Move propagated-inputs to inputs.

* gnu/packages/music.scm (beets)[propagated-inputs]: Replace with ...
[inputs]: ... new field.

gnu/packages/music.scm

@@ -1508,7 +1508,7 @@ (define-public beets
        ("python2-rarfile" ,python2-rarfile)
        ("python2-responses" ,python2-responses)))
     ;; TODO: Install optional plugins and dependencies.
-    (propagated-inputs
+    (inputs
      `(("python2-enum34" ,python2-enum34)
        ("python2-jellyfish" ,python2-jellyfish)
        ("python2-munkres" ,python2-munkres)