Do not try to remove a db record unless it's an UNLINK event.

When using changelog with Lustre, if a file doesn't exists anymore on the filesystem, we'll get an UNLINK record eventually.
If a file has been removed from the filesystem, and we get some record related to it (such as ATIME, CLOSE, ...), the pipeline tries to delete the record, which lead to the following error:

  ... [23133/4]: ListMgr | Missing mandatory attribute name to ListMgr_Remove
  ... [23133/4]: EntryProc | Error 12 performing database operation.

There's no need to complicate the pipeline, since at some point an UNLINK event will happen, so just ignore that record.
Enlarge some strings.