No more use of MACOSX_SDK_VERSION outside configure.ac

...after <https://gerrit.libreoffice.org/60376> "Remove
Library_avmediaQuickTime, which is dead" and
<https://gerrit.libreoffice.org/60377> "Remove MACOSX_SDK_VERSION < 101200 code,
which is dead".  (This commit can be reverted if MACOSX_SDK_VERSION ever needs
to be used again in makefiles or source code.)

Change-Id: Iaff300d325e357f96c329cc84b3b37d91863d4b0
Reviewed-on: https://gerrit.libreoffice.org/60378
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

config_host.mk.in

@@ -381,7 +381,6 @@ export MACOSX_CODESIGNING_IDENTITY=@MACOSX_CODESIGNING_IDENTITY@
 export MACOSX_DEPLOYMENT_TARGET=@MACOSX_DEPLOYMENT_TARGET@
 export MACOSX_PACKAGE_SIGNING_IDENTITY=@MACOSX_PACKAGE_SIGNING_IDENTITY@
 export MACOSX_SDK_PATH=@MACOSX_SDK_PATH@
-export MACOSX_SDK_VERSION=@MACOSX_SDK_VERSION@
 export MAC_OS_X_VERSION_MAX_ALLOWED=@MAC_OS_X_VERSION_MAX_ALLOWED@
 export MAC_OS_X_VERSION_MIN_REQUIRED=@MAC_OS_X_VERSION_MIN_REQUIRED@
 export MAC_OS_X_VERSION_MIN_REQUIRED_DOTS=@MAC_OS_X_VERSION_MIN_REQUIRED_DOTS@

configure.ac

@@ -2920,7 +2920,6 @@ if test $_os = Darwin -o $_os = iOS; then
     AC_MSG_RESULT([$MACOSX_BUNDLE_IDENTIFIER])
 fi
 AC_SUBST(MACOSX_SDK_PATH)
-AC_SUBST(MACOSX_SDK_VERSION)
 AC_SUBST(MACOSX_DEPLOYMENT_TARGET)
 AC_SUBST(MAC_OS_X_VERSION_MIN_REQUIRED)
 AC_SUBST(MAC_OS_X_VERSION_MIN_REQUIRED_DOTS)

solenv/gbuild/platform/macosx.mk

@@ -40,7 +40,6 @@ gb_OSDEFS := \
 	-DNO_PTHREAD_PRIORITY \
 	-DMAC_OS_X_VERSION_MIN_REQUIRED=$(MAC_OS_X_VERSION_MIN_REQUIRED) \
 	-DMAC_OS_X_VERSION_MAX_ALLOWED=$(MAC_OS_X_VERSION_MAX_ALLOWED) \
-	-DMACOSX_SDK_VERSION=$(MACOSX_SDK_VERSION) \
 	$(LFS_CFLAGS) \