tests: remove a redundant texinfo test * t/txinfo-add-missing.sh: This one, its checks being already covered by the more extensive 't/add-missing.tap' test. * t/txinfo-add-missing2.sh: Rename ... * t/txinfo-add-missing-and-dist.sh: Like this. * t/list-of-tests.mk: Adjust. Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>