Remove the allowed_timestamp_delta from the BLF UT

Now that the BLF float arithmetic issue is fixed we no longer need to  tweek the `allowed_timestamp_delta` in the BLF unit tests

Author: pierreluctg

test/logformats_test.py

@@ -694,7 +694,6 @@ def _setup_instance(self):
             check_fd=True,
             check_comments=False,
             test_append=True,
-            allowed_timestamp_delta=1.0e-6,
             preserves_channel=False,
             adds_default_channel=0,
         )