Cleanup BOOST_SYSTEM_LIB after upgrade to boost 1.89

Fixup after 421a66fc52 which left some
BOOST_SYSTEM_LIB usage, breaking system-boost builds.

Change-Id: I64bdcc163a954927684a83bf1c1ef98238acf9c4
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/191078
Reviewed-by: Xisco Fauli <xiscofauli@libreoffice.org>
Reviewed-by: Thorsten Behrens <thorsten.behrens@collabora.com>
Tested-by: Jenkins

RepositoryExternal.mk

@@ -3404,7 +3404,6 @@ $(call gb_LinkTarget_add_libs,$(1),\
 
 $(if $(SYSTEM_BOOST), \
 	$(call gb_LinkTarget_add_ldflags,$(1),$(BOOST_LDFLAGS)) \
-	$(call gb_LinkTarget_add_libs,$(1),$(BOOST_SYSTEM_LIB)) \
 )
 
 endef

config_host.mk.in

@@ -48,7 +48,6 @@ export BOOST_DATE_TIME_LIB=@BOOST_DATE_TIME_LIB@
 export BOOST_FILESYSTEM_LIB=@BOOST_FILESYSTEM_LIB@
 export BOOST_IOSTREAMS_LIB=@BOOST_IOSTREAMS_LIB@
 export BOOST_LDFLAGS=@BOOST_LDFLAGS@
-export BOOST_SYSTEM_LIB=@BOOST_SYSTEM_LIB@
 export BOX2D_CFLAGS=@BOX2D_CFLAGS@
 export BOX2D_LIBS=@BOX2D_LIBS@
 export BRAND_INTRO_IMAGES=@BRAND_INTRO_IMAGES@

external/liborcus/ExternalProject_liborcus.mk

@@ -38,7 +38,7 @@ ifneq ($(SYSTEM_ZLIB),)
 liborcus_LIBS+=-lz
 endif
 ifneq ($(SYSTEM_BOOST),)
-liborcus_LIBS+=$(BOOST_SYSTEM_LIB) $(BOOST_IOSTREAMS_LIB) $(BOOST_FILESYSTEM_LIB)
+liborcus_LIBS+=$(BOOST_IOSTREAMS_LIB) $(BOOST_FILESYSTEM_LIB)
 else
 liborcus_LIBS+=-L$(gb_StaticLibrary_WORKDIR) -lboost_iostreams -lboost_filesystem
 endif

m4/ax_boost_filesystem.m4

@@ -63,10 +63,6 @@ AC_DEFUN([AX_BOOST_FILESYSTEM],
 		LDFLAGS="$LDFLAGS $BOOST_LDFLAGS"
 		export LDFLAGS
 
-		LIBS_SAVED=$LIBS
-		LIBS="$LIBS $BOOST_SYSTEM_LIB"
-		export LIBS
-
         AC_CACHE_CHECK(whether the Boost::Filesystem library is available,
 					   ax_cv_boost_filesystem,
         [AC_LANG_PUSH([C++])
@@ -113,6 +109,5 @@ AC_DEFUN([AX_BOOST_FILESYSTEM],
 
 		CPPFLAGS="$CPPFLAGS_SAVED"
 		LDFLAGS="$LDFLAGS_SAVED"
-		LIBS="$LIBS_SAVED"
 	fi
 ])