[v3,trunk] disable a concept check for std::transform

[Gabriel Dos Reis]

Phil Edwards <pedwards@disaster.jaj.com> writes:

| Thanks to some prompting by Peter Schmid, one of the tests being done in the
| (old and new) checks was discovered to be too strict.  I fear the correct
| method is going to require some hefty cleverness, and as such we're not
| going to do it until it's clever *and clean and sensible*.
| 
| Tested and applied to trunk.

Please, could remove the corresponding piece of code on branch as well?

Thanks,

-- Gaby