Remove "Remove duplication of test setup" from the todo list.

Remove "Remove duplication of test setup" from the todo list.

It's no longer obvious which files in t/ contain significant amounts of
setup code which is duplicated. Common cases of skip logic have already been
moved into t/test.pl. The suggestion of replacing $Is_Foo checks with %Is is
not a clear-cut win - each $Is_Foo eliminated is only a 1 line saving, at the
cost of another testing idiom the future maintenance programmer has to become
familiar with.

The related suggestion "Migrate t/ from custom TAP generation" remains
something to do. There are still various files in t/ which could use be
converted to use the comparison functions of t/test.pl reducing code size,
improving failure diagnostics and where this eliminates manual test counters,
increasing flexibility for adding tests in the logically correct location
within the file.