Don't enable fsync in src/test/recovery/t/008_fsm_truncation.pl.

Don't enable fsync in src/test/recovery/t/008_fsm_truncation.pl.

In adverse circumstances, the fsync calls cause this test to run for
quite a long time (multiple minutes) and even suffer timeout failures.
This seems to date from before we made an effort to disable fsync in
all our test cases; there's not a lot of point in using it if there's
not a plan to force an O/S crash during the test.

Discussion: https://postgr.es/m/440239.1642560607@sss.pgh.pa.us