ext4: remove unused enum EXT4_FC_COMMIT_FAILED

Below commit removed all references of EXT4_FC_COMMIT_FAILED.
commit 0915e464 ("ext4: simplify updating of fast commit stats")

Just remove it since it is not used anymore.
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/c941357e476be07a1138c7319ca5faab7fb80fc6.1647057583.git.riteshh@linux.ibm.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/fast_commit.h

@@ -93,7 +93,6 @@ enum {
 	EXT4_FC_REASON_RENAME_DIR,
 	EXT4_FC_REASON_FALLOC_RANGE,
 	EXT4_FC_REASON_INODE_JOURNAL_DATA,
-	EXT4_FC_COMMIT_FAILED,
 	EXT4_FC_REASON_MAX
 };