Fix build breakage on Linux

Remove usage of constant strings for maintaining file deletion queue

Change-Id: I1992343ff65f923b6d3ffbf7a25932b936e3ff7c
Reviewed-on: http://review.couchbase.org/41291
Reviewed-by: Sundararaman Sridharan <sundar@couchbase.com>
Tested-by: Sriram Ganesan <sriram@couchbase.com>