Revert "wrap conflicts checking in a TODO, as the failure cannot always be fixed before/during installation"

This reverts commit ce6b6f76dd46123b9060a5debcc396bcf81e8978.

This was my mistake in confusing the meaning of 'conflict' from
CPAN::Meta::Spec and 'conflict' from Dist::CheckConflicts.  This dist checks
the former, *not* the latter. The prereq type of conflict should absolutely be
a test failure: it is a "cannot be installed", not "update this afterwards".