Extract trivial omnitigs that are not subwalks of non-trivial omnitigs

[sebschmi]

• plan how to do this
• algorithm:
  • keep a bitvector to mark edges as used
  • mark edges from non-trivial omnitigs as used
  • iterate over all edges and if unused and in a maximal trivial heart compute their univocal extension
  • mark all edges on the univocal extension as used
• write a test case on a graph with a few non-trivial omnitigs as well.