contrib: libaribcaption: don't force DirectWrite option

It's automatically enabled for Windows targets and not used otherwise.

contrib/src/libaribcaption/rules.mak

@@ -11,18 +11,14 @@ LIBARIBCC_WITH_FREETYPE = 1
 
 ifdef HAVE_ANDROID
 LIBARIBCC_WITH_FONTCONFIG = 0
-LIBARIBCC_WITH_DIRECTWRITE = 0
 else
 ifdef HAVE_DARWIN_OS
 LIBARIBCC_WITH_FONTCONFIG = 0
-LIBARIBCC_WITH_DIRECTWRITE = 0
 else
 ifdef HAVE_WIN32
 LIBARIBCC_WITH_FONTCONFIG = 0
-LIBARIBCC_WITH_DIRECTWRITE = 1
 else
 LIBARIBCC_WITH_FONTCONFIG = 1
-LIBARIBCC_WITH_DIRECTWRITE = 0
 endif
 endif
 endif
@@ -61,10 +57,6 @@ else
 LIBARIBCC_CONF += -DARIBCC_USE_FONTCONFIG:BOOL=OFF
 endif
 
-ifeq ($(LIBARIBCC_WITH_DIRECTWRITE), 1)
-LIBARIBCC_CONF += -DARIBCC_USE_DIRECTWRITE:BOOL=ON
-endif
-
 
 .libaribcaption: libaribcaption toolchain.cmake
 	cd $< && rm -f CMakeCache.txt