Remove files that seems to be unnecessary.

TODO
-> Contents are not updated, and the contents should be managed in the issue of GitHub.

t/00test_harness_check.t
-> Test::Harness 2.03 is specified in PREREQ_PM of Makefile.PL, and if perl 5.8.1 or higher,
    Test::Harness 2.30 or higher is installed always, this test is sure to succeed.

t/pod-coverage.t
-> It is like to be always skipped.
I suspect and should delete this test.
Or, should it be like to run only when the AUTHOR_TESTING is specified?
(But, coverage of the pod is not 100% at present, the test. Fail)