Rename misc uses of "free"

In preparation for fixing https://github.com/harfbuzz/harfbuzz/issues/3044

src/hb-cache.hh

diff --git a/src/hb-cache.hh b/src/hb-cache.hh
index bf26d96..e617b75 100644
--- a/src/hb-cache.hh
+++ b/src/hb-cache.hh
@@ -30,7 +30,7 @@
 #include "hb.hh"
 
 
-/* Implements a lock-free cache for int->int functions. */
+/* Implements a lockfree cache for int->int functions. */
 
 template <unsigned int key_bits, unsigned int value_bits, unsigned int cache_bits>
 struct hb_cache_t