tests: avoid spurious failures when @MKDIR_P@ points to "install-sh -d"

tests: avoid spurious failures when @MKDIR_P@ points to "install-sh -d"

* t/self-check-cleanup.tap: Several checks in this test were failing on
NetBSD 5.1.  That happened because on that system, '@MKDIR_P@' expands to
an "install-sh -d" invocation that references the $(builddir), and the
code trying to duplicate some of the Automake testsuite infrastructure
in the test subdirectory of this self test wasn't smart enough to cater
to that situation.  Granted, we could tweak the test case once more to
fix this Yet Another Spurious Failure, but at this point it has become
clear that the extra coverage offered by this test is not worth all the
hassle.  Just remove the test.  Since the testsuite is regularly run on
several systems and with different setups, most issues with the testsuite
framework will reveal themselves anyway; no actual need to unit-test them
in our testsuite, if that's too tricky.
* t/list-of-tests.mk: Adjust.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>