DOCS-249-related: delete fsync glossary entry

Author: Bob Grabar

source/reference/glossary.txt

@@ -366,10 +366,6 @@ Glossary
       migration of :term:`chunks <chunk>`. Administrators must disable
       the balancer for all maintenance operations on a sharded cluster.
 
-   fsync
-      A system call that flushes all dirty, in-memory pages to disk. MongoDB
-      calls ``fsync()`` every 60 seconds.
-
    chunk
       In the context of a :term:`sharded cluster`, a chunk is a contiguous
       range of :term:`shard key` values assigned to a particular :term:`shard`.