[mutex] Add constructor/destructor

Use in one place.

src/hb-mutex.hh

@@ -97,6 +97,9 @@ struct hb_mutex_t
   /* Create space for, but do not initialize m. */
   alignas(hb_mutex_impl_t) char m[sizeof (hb_mutex_impl_t)];
 
+  hb_mutex_t () { init (); }
+  ~hb_mutex_t () { fini (); }
+
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wcast-align"
   void init   () { hb_mutex_impl_init   ((hb_mutex_impl_t *) m); }

src/hb-subset-accelerator.hh

@@ -88,10 +88,7 @@ struct hb_subset_accelerator_t
     destroy_cmap_cache(nullptr),
     has_seac(has_seac_),
     cff_accelerator(nullptr),
-    destroy_cff_accelerator(nullptr)
-  {
-    sanitized_table_cache_lock.init ();
-  }
+    destroy_cff_accelerator(nullptr) {}
 
   ~hb_subset_accelerator_t ()
   {
@@ -100,8 +97,6 @@ struct hb_subset_accelerator_t
 
     if (cmap_cache && destroy_cmap_cache)
       destroy_cmap_cache ((void*) cmap_cache);
-
-    sanitized_table_cache_lock.fini ();
   }
 
   // Generic