HPCC-9802 Delete logical file using removeEntry(), not detach()

Existing ECLWatch code deletes a logical file using detach(). When
the file is associated with a superfile, the superfile may not be
able to be deleted. This fix calls removeEntry() to delete a file.
The removeEntry() should check whether the file can be deleted or
not if it is a subfile. This fix also cleans the code.

Signed-off-by: Kevin Wang <kevin.wang@lexisnexis.com>