btrfs: remove useless comments

btrfs: remove useless comments

Remove comments from the new test template that are not relevant once
the test case is written:

- commented out common.filters (no filters used)
- Import common functions.
- real QA test starts here
- Modify as appropriate.
- get standard environment, filters and checks

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>