gnu: txr: Fix license installation.

The install-license-files phase was installing LICENSE-CYG when it
shouldn't have, because that license applies only to TXR builds for
Microsoft Windows; and it was also ignoring the METALICENSE file.
However, TXR's Makefile was already installing the LICENSE and
METALICENSE files into share/txr (the datadir), so redirect them into
the appropriate doc directory and delete the install-license-files
phase.

* gnu/packages/lisp.scm (txr)[arguments]<#:phases>
  {fix-license-installation}: New phase.
  {install-license-files}: Delete phase.

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

gnu/packages/lisp.scm

@@ -931,6 +931,15 @@ the HTML documentation of TXR.")
        #:test-target "tests"
        #:phases
        (modify-phases %standard-phases
+         (add-after 'unpack 'fix-license-installation
+           (lambda* (#:key outputs #:allow-other-keys)
+             (substitute* "Makefile"
+               (("INSTALL(,.*LICENSE,.*)\\$\\(datadir\\)" _ match)
+                (string-append "INSTALL" match
+                               (assoc-ref outputs "out")
+                               "/share/doc/" ,name "-" ,version)))
+             #t))
+         (delete 'install-license-files)
          (add-after 'unpack 'inhibit-doc-syms-generation
            (lambda _
              (substitute* "genman.txr"