core: use C++-primitives for g_tag_list

The old code was leaking memory. Use std::unique_ptr<> for
ownership management.

This is still very primitive and divetags are kept during
application lifetime. There should probably be some form
of reference counting. And the taglist should not be global,
but attached to the divelog.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/qthelper.cpp

@@ -1229,12 +1229,6 @@ QStringList get_dive_gas_list(const struct dive *d)
 	return list;
 }
 
-QString get_taglist_string(struct tag_entry *tag_list)
-{
-	std::string tags = taglist_get_tagstring(tag_list);
-	return QString::fromStdString(tags);
-}
-
 QStringList stringToList(const QString &s)
 {
 	QStringList res = s.split(",", SKIP_EMPTY);