We have code in order to remove deltas when removing a package, but it
is never run, since we try to remove the wrong file.
This was broken in commit cb0f2bd0385f447e045e2b2aab9ffa55df3c2d8a which
modified the internal layout we use to modify the db, changing "tree" to
"db", but did not update all locations where it was used.
This worked swimmingly well as long as only repo-add updates were
handling the backup and restoral of the delta file, as the delta file
therefore got backed up to the correct location (db) in the shared
db_remove_entry() function.
But later on in the repo-remove logic, we tried removing a different
file that will never exist (tree).
Fixes FS#53041
Signed-off-by: Eli Schwartz