Ensure S3 storage service only cleans files marked deleted

There was a bug in the initial implementation of the S3 object storage
service in 65c5f29: "Move private storage to S3-backed implementation"
which allows `cleanFile()` to clean files which aren't marked as
deleted. This isn't a significant issue since we don't currently rely on
it only functioning on files marked deleted, but the latter behavior is
in the API documentation, consistent with how the sister function
`cleanAllFiles()` behaves, and helpful for preventing accidental file
deletions, so we should fix it.

Author: lberrymage

console/src/main/kotlin/app/accrescent/parcelo/console/storage/S3ObjectStorageService.kt

@@ -94,7 +94,9 @@ class S3ObjectStorageService(
     }
 
     override suspend fun cleanObject(id: Int) {
-        val file = transaction { File.findById(id) } ?: return
+        val file = transaction {
+            File.find { Files.id eq id and (deleted eq true) }.singleOrNull()
+        } ?: return
         val s3ObjectKey = file.s3ObjectKey
 
         S3Client {