[config] Add HB_NO_VAR to disable variations support, enabled by HB_TINY

Part of https://github.com/harfbuzz/harfbuzz/issues/1652
diff --git a/src/hb-config.hh b/src/hb-config.hh
index 3f9a9ca..8f78ede 100644
--- a/src/hb-config.hh
+++ b/src/hb-config.hh
@@ -69,6 +69,7 @@
 #define HB_NO_OT_SHAPE_FRACTIONS
 #define HB_NO_STAT
 #define HB_NO_SUBSET_LAYOUT
+#define HB_NO_VAR
 #endif
 
 #ifdef HB_MINI