Do not fsync profiles on close

There's no need to fsync profile data right away. We get
many chances to write it again in case something goes
wrong. We can rely on a simple close(), no sync, and let
the kernel decide when to write to disk. This should
improve the I/O behavior of saving profiles.

Bug: 36817443
Test: m test-art-host-gtest
Change-Id: I0df27947006d57b15d6311420c79288148736f62