Enable more compiler warnings in tests/Makefile

tests/Makefile had some unused warnings disabled unnecessarily, which
test-ref-configs.pl was turning back on. We don't need to disable these warnings
so I'm turning them back on.
diff --git a/tests/Makefile b/tests/Makefile
index b6e49bf..5e4fa13 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -3,7 +3,7 @@
 # To compile with PKCS11: add "-lpkcs11-helper" to LDFLAGS
 
 CFLAGS	?= -O2
-WARNING_CFLAGS ?= -Wall -W -Wdeclaration-after-statement -Wno-unused-function -Wno-unused-value
+WARNING_CFLAGS ?= -Wall -W -Wdeclaration-after-statement -Wunused
 LDFLAGS ?=
 
 LOCAL_CFLAGS = $(WARNING_CFLAGS) -I../include -D_FILE_OFFSET_BITS=64