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>

subsurface-downloader-main.cpp

@@ -110,7 +110,6 @@ int main(int argc, char **argv)
 		printf("Give a log file name as argument, or configure a cloud URL.\n");
 	}
 	clear_divelog(&divelog);
-	taglist_free(g_tag_list);
 	parse_xml_exit();
 
 	// Sync struct preferences to disk