Move extent2 -> extent.

Eventually, we may fully break off the extent module; but not for some time.  If
it's going to live on in a non-transitory state, it might as well have the nicer
name.

include/jemalloc/internal/extent.h

@@ -1,5 +1,5 @@
-#ifndef JEMALLOC_INTERNAL_EXTENT2_H
-#define JEMALLOC_INTERNAL_EXTENT2_H
+#ifndef JEMALLOC_INTERNAL_EXTENT_H
+#define JEMALLOC_INTERNAL_EXTENT_H
 
 #include "jemalloc/internal/ecache.h"
 #include "jemalloc/internal/ehooks.h"
@@ -10,11 +10,6 @@
  * This module contains the page-level allocator.  It chooses the addresses that
  * allocations requested by other modules will inhabit, and updates the global
  * metadata to reflect allocation/deallocation/purging decisions.
- *
- * The naming ("extent2" for the module, and "extent_" or "extents_" for most of
- * the functions) is historical.  Eventually, the naming should be updated to
- * reflect the functionality.  Similarly, the utilization stats live here for no
- * particular reason.  This will also be changed, but much more immediately.
  */
 
 /*
@@ -61,4 +56,4 @@ bool extent_merge_wrapper(tsdn_t *tsdn, ehooks_t *ehooks,
 
 bool extent_boot(void);
 
-#endif /* JEMALLOC_INTERNAL_EXTENT2_H */
+#endif /* JEMALLOC_INTERNAL_EXTENT_H */

include/jemalloc/internal/jemalloc_internal_inlines_b.h

@@ -1,7 +1,7 @@
 #ifndef JEMALLOC_INTERNAL_INLINES_B_H
 #define JEMALLOC_INTERNAL_INLINES_B_H
 
-#include "jemalloc/internal/extent2.h"
+#include "jemalloc/internal/extent.h"
 #include "jemalloc/internal/rtree.h"
 
 /* Choose an arena based on a per-thread value. */