ext4: remove unused EXT_STATS macro from ext4_extents.h

The EXT_STATS macro in fs/ext4/ext4_extents.h has been defined
but never used in the codebase since its introduction. This patch
removes it.

Analysis:
1. No references found in fs/ext4/ or other kernel code.
2. No impact on compilation or functionality.
3. Git history shows it was never utilized.

Signed-off-by: Baolin Liu <[e-mail]>
Reviewed-by: Baokun Li <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Theodore Ts'o <[e-mail]>

fs/ext4/ext4_extents.h

···
 #define CHECK_BINSEARCH__
 
 /*
- * If EXT_STATS is defined then stats numbers are collected.
- * These number will be displayed at umount time.
- */
-#define EXT_STATS_
-
-
-/*
  * ext4_inode has i_block array (60 bytes total).
  * The first 12 bytes store ext4_extent_header;
  * the remainder stores an array of ext4_extent.