Wish there was some admin tool that would search the mdl_files table, but don't think there is at this point.
Before doing anything like what is suggested below, run a complete backup: data directory and db.
In the DB:
select * from `mdl_files` where (`filename` like "%backup%" and `filename` like "%.zip%")
Will show if there are any 1.9 backup zips. Will also show the hash information from which one could decifer the directory locations in filedir folder of data folder.
Example:
Found in a MDL 2 site that has backup-blah.zip's from a 1.9:
| 89bd873322c3180daddca152afd4fb8517f775b9 | 4c4fcbf0c12471867ae1eaa0dde8253c6ee04910 | 274 | backup | course | 0 | / | backup-bma-NOUSERS-20100119-1029.zip | 10189821 | application/zip |
0
|
89bd873322c3180daddca152afd4fb8517f775b9 (content hash)
Indicates a folder 89 and contained there in a bd folder.
/path_to_data/moodle2data/filedir/89/bd
shows a file:
-rw-rw-rw- 1 apache apache 10189821 Apr 28 2011 89bd873322c3180daddca152afd4fb8517f775b9
As long as there is no link to the file in a course, could manually remove the folders and hash file (really the backup-blah.zip) as well as removing the record(s) from the table to 'tidy up'.
'spirit of sharing', Ken