gnu: tuxguitar: Use "modify-phases" syntax.

* gnu/packages/music.scm (tuxguitar)[arguments]: Use "modify-phases"
  syntax.

gnu/packages/music.scm

@@ -701,8 +701,9 @@ is subjective.")
        #:tests? #f ;no "check" target
        #:parallel-build? #f ;not supported
        #:phases
-       (alist-cons-before
-        'build 'enter-dir-set-path-and-pass-ldflags
+       (modify-phases %standard-phases
+         (delete 'configure)
+         (add-before 'build 'enter-dir-and-set-flags
           (lambda* (#:key inputs #:allow-other-keys)
             (chdir "TuxGuitar")
             (substitute* "GNUmakefile"
@@ -710,8 +711,7 @@ is subjective.")
                (string-append "PROPERTIES?= -Dswt.library.path="
                               (assoc-ref inputs "swt") "/lib"))
               (("\\$\\(GCJ\\) -o") "$(GCJ) $(LDFLAGS) -o"))
-          #t)
-        (alist-delete 'configure %standard-phases))))
+            #t)))))
     (inputs
      `(("swt" ,swt)))
     (native-inputs