lavf/matroskaenc: use mkv_check_tag_name consistently

Previously, we used a different list of checks when deciding whether to
write a set of tags at all than we did when deciding whether to write an
individual tag in the set. This resulted in sometimes writing an empty
tag master and seekhead. Now we use mkv_check_tag_name everywhere, so
if a dictionary is entirely composed of tags we skip, we don't write a
tag master at all.

This affected the test file, since "language" was on one list but not
the other, so we were writing an empty tag master there. The test hash
is updated to reflect that change.
