testsuite: use TAP for `depmod*' tests, related simplifications

testsuite: use TAP for `depmod*' tests, related simplifications

* tests/depmod-tests.sh: Delete this complex and multifarious
script, moving all it checks it used to perform into ...
* tests/depmod.tap: ... this TAP-based test script.  And extend
it quite a bit, since the new form of the test was papering over
some pre-existing failures (this was due to the fact that the
values used for the VPATH were shorter in the new test script).
* tests/depmod-data.test: Deleted.
* tests/Makefile.am ($(srcdir)/depmod-tests.am): Don't include
nor generate it anymore.
(EXTRA_DIST): Don't distribute depmod-tests.sh anymore.
(TEST_EXTENSIONS): Remove '.depmod'.
(DEPMOD_LOG_COMPILER): Deleted.
(depmod-data.log, $(depmod_tests:.depmod=.log)): Delete
dependencies for these files, which are not used anymore.
($(depmod_tests)): Delete this dummy dependency declaration.
(TESTS): Remove $(depmod_tests).
(handwritten_tests): Remove depmod-data.test, add depmod.tap.
* bootstrap: Don't generate tests/depmod-tests.am anymore.