remove unused fields from OS thread local data

include/mimalloc-types.h

@@ -380,12 +380,8 @@ typedef struct mi_segments_tld_s {
 } mi_segments_tld_t;
 
 // OS thread local data
-typedef struct mi_os_tld_s {
-  uintptr_t           mmap_next_probable;  // probable next address start allocated by mmap (to guess which path to take on alignment)
-  void*               mmap_previous;       // previous address returned by mmap
-  uint8_t*            pool;                // pool of segments to reduce mmap calls on some platforms
-  size_t              pool_available;      // bytes available in the pool
-  mi_stats_t*         stats;               // points to tld stats
+typedef struct mi_os_tld_s {  
+  mi_stats_t*         stats;        // points to tld stats
 } mi_os_tld_t;
 
 // Thread local data

src/alloc.c

@@ -237,7 +237,7 @@ void mi_free(void* p) mi_attr_noexcept
 #endif
 
   uintptr_t tid = _mi_thread_id();
-  if (mi_likely(tid == page->flags)) {  
+  if (mi_likely(tid == page->flags)) {  // if equal, the thread id matches and it is not a full page, nor has aligned blocks
     // local, and not full or aligned
     mi_block_t* block = (mi_block_t*)p;
     mi_block_set_next(page, block, page->local_free);  

src/init.c

@@ -98,8 +98,8 @@ static mi_tld_t tld_main = {
   0,
   &_mi_heap_main,
   { { NULL, NULL }, {NULL ,NULL}, 0, 0, 0, 0, 0, 0, NULL, tld_main_stats }, // segments
-  { 0, NULL, NULL, 0, tld_main_stats },          // os
-  { MI_STATS_NULL }                              // stats
+  { tld_main_stats },          // os
+  { MI_STATS_NULL }            // stats
 };
 
 mi_heap_t _mi_heap_main = {