gnu: giac-xcas: Rename to "giac" to match upstream name.

* gnu/packages/algebra.scm (giac): New variable.
(giac-xcas): Deprecate.

gnu/packages/algebra.scm

@@ -247,9 +247,9 @@ precision.")
    (license license:gpl3+)
    (home-page "http://cmh.gforge.inria.fr/")))
 
-(define-public giac-xcas
+(define-public giac
   (package
-    (name "giac-xcas")
+    (name "giac")
     (version "1.5.0-49")
     (source (origin
               (method url-fetch)
@@ -336,6 +336,9 @@ maple, mupad and the TI89.  It is available as a standalone program (graphic
 or text interfaces) or as a C++ library.")
     (license license:gpl3+)))
 
+(define-public giac-xcas
+  (deprecate-package "giac-xcas" giac))
+
 (define-public flint
   (package
    (name "flint")