Revert "Don't export zlib symbols"

Not needed after having fixed the MinGW visibility checks.

This reverts commit 2f0b0e54.

tools/Library_tl.mk

@@ -106,14 +106,6 @@ $(eval $(call gb_Library_use_external,tl,zlib))
 
 ifeq ($(OS),WNT)
 
-ifeq ($(COM),GCC)
-
-$(eval $(call gb_Library_add_libs,tl,\
-    -Wl$(COMMA)--exclude-libs=libzlib.a \
-))
-
-endif
-
 $(eval $(call gb_Library_set_include,tl,\
     -I$(SRCDIR)/tools/win/inc \
     $$(INCLUDE) \