ghostscript: remove legacy patch png_mak.patch

ghostscript: remove legacy patch png_mak.patch

png_mak.patch was created for ghostscript 9.16 and causes make circular
dependency now. Check source code base/png.mak after apply png_mak.patch:

Line 77: $(MAKEDIRS) : $(pnglibconf_h)
Line 83: $(pnglibconf_h) : $(PNGSRC)scripts$(D)pnglibconf.h.prebuilt $(TOP_MAKEFILES) $(MAKEDIRS)

So remove png_mak.patch.

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>