Remove unnecessary step in "Get the strongest metadata from set"

The invalid ni URLs are already filtered out in the "Parse
metadata" algorithm.
Remove unnecessary step "Does resource match metadataList"

This step is not needed because the "Get the strongest metadata
from set" algorithm would only return an empty string if the
"Parse metadata" return an empty set. If that were the case, we
would never get to this step and instead would exit the algorithm
at Step 4.
Remove second unnecessary step in "Does resource match metadataList"

As of 7d0c06e7d73d2d80a570c97ccc517ad084f74bfc, the "Apply
algorithm to resource" algorithm never returns null.
Merge pull request #96 from fmarier/remove-more-unnecessary-steps

Remove more unnecessary steps