Use the flat bitmap for eset and psset bitmaps.

This is simpler (note that the eset field comment was actually incorrect!), and
slightly faster.

include/jemalloc/internal/eset.h

@@ -2,7 +2,7 @@
 #define JEMALLOC_INTERNAL_ESET_H
 
 #include "jemalloc/internal/atomic.h"
-#include "jemalloc/internal/bitmap.h"
+#include "jemalloc/internal/flat_bitmap.h"
 #include "jemalloc/internal/edata.h"
 #include "jemalloc/internal/mutex.h"
 
@@ -22,7 +22,7 @@ struct eset_s {
 	atomic_zu_t nbytes[SC_NPSIZES + 1];
 
 	/* Bitmap for which set bits correspond to non-empty heaps. */
-	bitmap_t bitmap[BITMAP_GROUPS(SC_NPSIZES + 1)];
+	fb_group_t bitmap[FB_NGROUPS(SC_NPSIZES + 1)];
 
 	/* LRU of all extents in heaps. */
 	edata_list_inactive_t lru;

include/jemalloc/internal/psset.h

@@ -56,7 +56,8 @@ struct psset_s {
 	 * free run of pages in a pageslab.
 	 */
 	hpdata_age_heap_t pageslabs[PSSET_NPSIZES];
-	bitmap_t bitmap[BITMAP_GROUPS(PSSET_NPSIZES)];
+	/* Bitmap for which set bits correspond to non-empty heaps. */
+	fb_group_t bitmap[FB_NGROUPS(PSSET_NPSIZES)];
 	/*
 	 * The sum of all bin stats in stats.  This lets us quickly answer
 	 * queries for the number of dirty, active, and retained pages in the