gnu: vapoursynth: Make python a regular input.

This follows up on c00b1760f6, although
meson-build-system's lack of cross-compilation makes it theoretical.

* gnu/packages/video.scm (vapoursynth)[native-inputs]: Move python from
here…
[inputs]: …to here.

gnu/packages/video.scm

@@ -2835,11 +2835,11 @@ (define-public vapoursynth
        ("cython" ,python-cython)
        ("libtool" ,libtool)
        ("pkg-config" ,pkg-config)
-       ("python" ,python)
        ("yasm" ,yasm)))
     (inputs
      `(("ffmpeg" ,ffmpeg)
        ("libass" ,libass)
+       ("python" ,python)
        ("tesseract-ocr" ,tesseract-ocr)
        ("zimg" ,zimg)))
     (home-page "http://www.vapoursynth.com/")