Revert "Validation{Chain,Processor}: use new .failOnError() method"

This reverts commit 167a5edf3b74450a2fdeaaa156a31fe94c6f763b.

The problem is that in this case, we lose syntax error messages. This may not be
what is desired at this point.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
ValidationChain: remove an unneeded concrete type declaration

ProcessingReport has .mergeWith() now, and it works accurately.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>