Bug 10539: Followup for removing KohaTest unit tests

Bug 10539: Followup for removing KohaTest unit tests

Makefile.PL: Section for creating file t/test-config.txt removed.
Removes t/Makefile and t/rewrite-config-test too.
Modifies XISBN.t to remove two commented lines.

Test plan:
Grep for KohaTest, database_dependent, config-test, t/Makefile.
Run perl Makefile.PL and include running the test suite.
This may fail on t/00-valid-xml.t and t/QueryParser.t, but that is not the
result of this patch. Same for t/00-load.t with potential error on
Koha::Plugins::Base.
I had this result:

Test Summary Report:
t/00-valid-xml.t                  (Wstat: 1792 Tests: 381 Failed: 7)
  Failed tests:  10, 30-31, 169, 181, 201-202
  Non-zero exit status: 7
t/QueryParser.t                   (Wstat: 512 Tests: 0 Failed: 0)
  Non-zero exit status: 2
  Parse errors: No plan found in TAP output
Files=92, Tests=12385, 45 wallclock secs ( 1.74 usr  0.15 sys + 26.61 cusr  1.92 csys = 30.42 CPU)
Result: FAIL
Failed 2/92 test programs. 7/12385 subtests failed.

Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
All tests pass, and I find no mention of the removed test code.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>