gnu: Remove duplicate libxml++ packages.

Reported-by: Guillaume Le Vaillant <glv@posteo.net>

* gnu/packages/engineering.scm (freecad)[inputs]:
Replace libxmlplusplus-2 with libxml++-2.
* gnu/packages/music.scm (tascam-gtk)[inputs]:
Replace libxmlplusplus with libxml++.
* gnu/packages/xml.scm (libxmlplusplus, libxmlplusplus-2.4):
Remove unused variables.

gnu/packages/engineering.scm

@@ -2415,7 +2415,7 @@ comments.")))
        ("libtheora" ,libtheora)
        ("libtiff" ,libtiff)
        ("libxi" ,libxi)
-       ("libxmlplusplus" ,libxmlplusplus)
+       ("libxml++" ,libxml++)
        ("libxmu" ,libxmu)
        ("lz4" ,lz4)
        ("netcdf" ,netcdf)

gnu/packages/music.scm

@@ -1895,7 +1895,7 @@ complete studio.")
        `(("liblo" ,liblo)
          ("gtkmm" ,gtkmm)
          ("alsa-lib" ,alsa-lib)
-         ("libxmlplusplus" ,libxmlplusplus-2.6)))
+         ("libxml++" ,libxml++-2)))
       (native-inputs
        `(("glib:bin" ,glib "bin")
          ("pkg-config" ,pkg-config)))

gnu/packages/xml.scm

@@ -294,81 +294,6 @@ formulas and hyperlinks to multiple worksheets in an Excel 2007+ XLSX file.")
     (license (list license:bsd-2
                    license:public-domain)))) ; third_party/md5
 
-;; This is the latest stable release.
-(define-public libxmlplusplus
-  (package
-    (name "libxmlplusplus")
-    (version "3.2.0")
-    (source (origin
-             (method git-fetch)
-             (uri (git-reference
-                   (url "https://github.com/libxmlplusplus/libxmlplusplus")
-                   (commit version)))
-             (file-name (git-file-name name version))
-             (sha256
-              (base32
-               "0wjz591rjlgbah7dcq8i0yn0zw9d62b7g6r0pppx81ic0cx8n8ga"))))
-    (build-system gnu-build-system)
-    (arguments
-     `(#:phases
-       (modify-phases %standard-phases
-         (add-after 'unpack 'fix-documentation
-           (lambda* (#:key inputs #:allow-other-keys)
-             (let ((xmldoc (string-append (assoc-ref inputs "docbook-xml")
-                                          "/xml/dtd/docbook"))
-                   (xsldoc (string-append (assoc-ref inputs "docbook-xsl")
-                                          "/xml/xsl/docbook-xsl-"
-                                          ,(package-version docbook-xsl))))
-               (substitute* '("examples/dom_xpath/example.xml"
-                              "docs/manual/libxml++_without_code.xml")
-                 (("http://.*/docbookx\\.dtd")
-                  (string-append xmldoc "/docbookx.dtd")))
-               (setenv "SGML_CATALOG_FILES"
-                       (string-append xmldoc "/catalog.xml"))
-               (substitute* "docs/manual/docbook-customisation.xsl"
-                 (("http://docbook.sourceforge.net/release/xsl/current/html/chunk.xsl")
-                  (string-append xsldoc "/html/chunk.xsl"))))
-             #t)))))
-    (propagated-inputs
-     `(("libxml2" ,libxml2)))
-    (inputs
-     `(("glibmm" ,glibmm)))
-    (native-inputs
-     `(("autoconf" ,autoconf)
-       ("automake" ,automake)
-       ("doxygen" ,doxygen)
-       ("docbook-xml" ,docbook-xml)
-       ("docbook-xsl" ,docbook-xsl)
-       ("graphviz" ,graphviz) ; for dot
-       ("libtool" ,libtool)
-       ("libxslt" ,libxslt)
-       ("mm-common" ,mm-common)
-       ("perl" ,perl)
-       ("pkg-config" ,pkg-config)))
-    (home-page "https://github.com/libxmlplusplus/libxmlplusplus/")
-    (synopsis "C++ bindings for libxml2")
-    (description
-     "libxml++ (a.k.a. libxmlplusplus) provides a C++ interface to XML files.
-It uses libxml2 to access the XML files.")
-    (license license:lgpl2.1+)))
-
-;; This is the last release providing the 2.6 API, hence the name.
-;; This is needed by tascam-gtk
-(define-public libxmlplusplus-2.6
-  (package
-    (inherit libxmlplusplus)
-    (name "libxmlplusplus")
-    (version "2.40.1")
-    (source (origin
-             (method git-fetch)
-             (uri (git-reference
-                   (url "https://github.com/libxmlplusplus/libxmlplusplus")
-                   (commit version)))
-             (file-name (git-file-name name version))
-             (sha256
-              (base32
-               "0gbfi4l88w828gmyc9br11l003ylyi4vigp5d1kfgsn0k4cig3y9"))))))
-
 (define-public python-libxml2
   (package/inherit libxml2
     (name "python-libxml2")