helpcompiler: evidently does not care that it uses UTF16 expat

... seeing as there isn't actually a handler in the compileExtensionHelp
function; possibly dead code there.

Change-Id: I96b3edff6be2d58d0c1852eb1043547c33e97c3a

helpcompiler/Library_helplinker.mk

@@ -46,7 +46,7 @@ $(eval $(call gb_Library_use_libraries,helplinker,\
 ))
 
 $(eval $(call gb_Library_use_externals,helplinker,\
-    expat_utf16 \
+    expat_utf8 \
     libxslt \
     libxml2 \
     clucene \