gnu: rtmidi: Remove custom bootstrap phase.

* gnu/packages/audio.scm (rtmidi)[arguments]: Remove autoconf phase.

gnu/packages/audio.scm

@@ -2285,19 +2285,15 @@ tempo and pitch of an audio recording independently of one another.")
     (build-system gnu-build-system)
     (arguments
      `(#:tests? #f ;no "check" target
-       #:phases (modify-phases %standard-phases
-                  (add-after
-                   'unpack 'autoconf
-                   (lambda _ (invoke "autoreconf" "-vfi")))
-                  (add-before
-                   'build 'fix-makefile
+       #:phases
+       (modify-phases %standard-phases
+         (add-before 'build 'fix-makefile
            (lambda _
              (substitute* "Makefile"
                (("/bin/ln") "ln")
                (("RtMidi.h RtError.h") "RtMidi.h"))
              #t))
-                  (add-before
-                   'install 'make-target-dirs
+         (add-before 'install 'make-target-dirs
            (lambda _
              (let ((out (assoc-ref %outputs "out")))
                (mkdir-p (string-append out "/bin"))