test: errors preparing for a test are not special

test: errors preparing for a test are not special

This script uses the following idiom to start each test in a known
good state:

	test_expect_success 'some commands use a pager' '
		rm -f paginated.out || cleanup_fail &&
		test_terminal git log &&
		test -e paginated.out
	'

where "cleanup_fail" is a function that prints an error message and
errors out.

That is bogus on three levels:

 - Cleanup commands like "rm -f" and "test_unconfig" are designed not
   to fail, so this logic would never trip.

 - If they were to malfunction anyway, it is not useful to set apart
   cleanup commands as a special kind of failure with a special error
   message.  Whichever command fails, the next step is to investigate
   which command that was, for example by running tests with
   "prove -e 'sh -x'", and fix it.

 - Relying on left-associativity of mixed &&/|| lists makes the code
   somewhat cryptic.

The fix is simple: drop the "|| cleanup_fail" in each test and the
definition of the "cleanup_fail" function so no new callers can arise.

Reported-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>