Do the @require@ and @diff@ comments in testsuite/27_io files do anything?

[Jonathan Wakely]

We have comments like these in a number of file I/O tests

e.g. testsuite/27_io/ios_base/sync_with_stdio/1.cc has:

// @require@ %-*.tst
// @diff@ %-*.tst %-*.txt

They suggest that the .txt file written by the test will be diffed
with a .tst reference file, but I don't think that diffing actually
happens.

Is this a remnant of an old testsuite?

Does it matter if we're not checking the file contents match?