view: actually omit subject text when dumping topics

view: actually omit subject text when dumping topics

Despite dump_topics() calling dedupe_subject() on the subject, the
index shows partly duplicated subjects, for example

  ` [PATCH 2/2] t/www_listing: avoid 'once' warnings
    ` [PATCH v2] t/www_listing: avoid 'once' warnings "

In the second line, the omission character " is appended, but the
entire subject is shown.  To display the subject with duplicated parts
omitted, regenerate it from the array that is modified by
dedupe_subject().