runtime.bash: remove outdated comment

Since commit 6e1d3752 ("tap13: list testcases individually") the
comment is no longer valid. Therefore let's remove it.

Reviewed-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Message-Id: <20200825102036.17232-2-mhartmay@linux.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>