[config] Disbale getenv() and atexit() if HB_LEAN

Part of https://github.com/harfbuzz/harfbuzz/issues/1652
diff --git a/src/hb-config.hh b/src/hb-config.hh
index 087e669..2eada98 100644
--- a/src/hb-config.hh
+++ b/src/hb-config.hh
@@ -42,8 +42,10 @@
 
 #ifdef HB_LEAN
 #define HB_DISABLE_DEPRECATED
+#define HB_NO_ATEXIT
 #define HB_NO_BITMAP
 #define HB_NO_CFF
+#define HB_NO_GETENV
 #define HB_NO_MATH
 #define HB_NO_OT_LAYOUT_UNUSED
 #endif