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.

(From OE-Core rev: 8a5890cc0b0a6c110edb36aec3614c3ebeb54e24)

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-extended/ghostscript/ghostscript/png_mak.patch

@@ -1,32 +0,0 @@
-ghostscript: add dependency for pnglibconf.h
-
-When using parallel make jobs, we need to be sure that
-pnglibconf.h is created before we try to reference it,
-so add a rule to png.mak.
-
-Upstream-Status: Pending
-
-Signed-off-by: Joe Slater <jslater@windriver.com>
-
-Rebase to 9.19
-Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
----
- base/png.mak | 2 ++
- 1 file changed, 2 insertions(+)
-
-diff --git a/base/png.mak b/base/png.mak
-index fe5c6e2..8abb53a 100644
---- a/base/png.mak
-+++ b/base/png.mak
-@@ -74,6 +74,8 @@ png.clean-not-config-clean :
- 
- pnglibconf_h=$(PNGGENDIR)$(D)pnglibconf.h
- 
-+$(MAKEDIRS) : $(pnglibconf_h)
-+
- png.config-clean :
- 	$(RM_) $(pnglibconf_h)
- 	$(RM_) $(PNGGEN)lpg*.dev
--- 
-2.8.1
-

meta/recipes-extended/ghostscript/ghostscript_9.21.bb

@@ -22,7 +22,6 @@ UPSTREAM_CHECK_REGEX = "(?P<pver>\d+(\.\d+)+)\.tar"
 SRC_URI_BASE = "https://github.com/ArtifexSoftware/ghostpdl-downloads/releases/download/gs921/${BPN}-${PV}.tar.gz \
                 file://ghostscript-9.15-parallel-make.patch \
                 file://ghostscript-9.16-Werror-return-type.patch \
-                file://png_mak.patch \
                 file://do-not-check-local-libpng-source.patch \
                 file://avoid-host-contamination.patch \
                 file://mkdir-p.patch \