Makefile: remove xref (not needed); use Dialyzer
diff --git a/Makefile b/Makefile
index ea76e54..be7f5ad 100644
--- a/Makefile
+++ b/Makefile
@@ -19,7 +19,7 @@
 all:
 	./rebar compile
 
-test: xref eunit
+test: eunit
 
 ci: clean debug test
 
@@ -31,9 +31,6 @@
 clean:
 	./rebar clean
 
-xref:
-	./rebar xref
-
 eunit:
 	./rebar eunit