btrfs: cleanup unused qgroup trace event

Commit 81fb6f77 (btrfs: qgroup: Add new trace point for
qgroup data reserve) added the following events which aren't used.
  btrfs__qgroup_data_map
  btrfs_qgroup_init_data_rsv_map
  btrfs_qgroup_free_data_rsv_map
So remove them.

CC: quwenruo@cn.fujitsu.com
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>