test-tool run-command testsuite: remove hardcoded filter

test-tool run-command testsuite: remove hardcoded filter

`test-tool run-command testsuite` currently assumes that it will only be
running the shell test suite, and therefore filters out anything that
does not match a hardcoded pattern of "t[0-9][0-9][0-9][0-9]-*.sh".

Later in this series, we'll adapt `test-tool run-command testsuite` to
also support unit tests, which do not follow the same naming conventions
as the shell tests, so this hardcoded pattern is inconvenient.

Since `testsuite` also allows specifying patterns on the command-line,
let's just remove this pattern. As noted in [1], there are no longer any
uses of `testsuite` in our codebase, it should be OK to break backwards
compatibility in this case. We also add a new filter to avoid trying to
execute "." and "..", so that users who wish to execute every test in a
directory can do so without specifying a pattern.

[1] https://lore.kernel.org/git/850ea42c-f103-68d5-896b-9120e2628686@gmx.de/

Signed-off-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>