t5570: drop racy test

t5570: drop racy test

t5570 being racy has been reported twice separately on the mailing
list [*1*, *2*].

To make the test race proof, we'd either have to introduce another
fifo the test snippet is waiting on, or somehow convincing "cat" to
flush (and let us know when it has).  Which really implies killing the
daemon, and wait()ing on cat to process the EOF and exit.  And that
makes the tests a lot more expensive if we have to start the daemon
for each snippet.

As this is a test for a relatively minor fix (according to the author)
in 19136be3f8 ("daemon: fix off-by-one in logging extended
attributes", 2018-01-24), drop it to avoid this racyness.  It doesn't
seem worth making the test code much more complex, or slowing down all
tests just to keep this one.

*1*: 1522783990.964448.1325338528.0D49CC15@webmail.messagingengine.com/
*2*: 9d4e5224-9ff4-f3f8-519d-7b2a6f1ea7cd@web.de

Reported-by: Jan Palus <jpalus@fastmail.com>
Reported-by: Torsten Bögershausen <tboegi@web.de>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>