Delete test testsuite-control-not-file; tag cannot be reproduced using dpkg-source.

The source tag 'debian-tests-control-is-not-a-regular-file' cannot be
tested using standard tools. The conditions that would be necessary
cause dpkg-source to abort with the message:

dpkg-source: error: test control debian/tests/control is not a regular file

The issue arose when the test was converted to standard tools.  (It
previously used pattern substitution.) Since most people use standard
tools, it makes little sense to pursue the test further.

Removes the test. If there is no other way to test the tag, the tag
may eventually also be removed from Lintian.

Gbp-Dch: ignore