title: Filter unique lines
body: <p>I have a tile type called fasta which contains a header "> 12122" followed by a string. I would like to remove duplicated strings in the file and keep only one of the duplicated string (same which) and the corresponding header.<br>
  In the example below the AGGTTCCGGATAAGTAAGAGCC is duplicated</p>
  
  <p>in:</p>
  
  <pre><code>&gt;17-46151
  AGGTTCCGGATAAGTAAGAGCC
  &gt;1-242
  AGGTTCCGGATAAGTAAGAGCC
  &gt;18-41148
  TCTTAACCCGGACCAGAAACTA
  &gt;43-16054
  GTCCCACTCCGTAGATCTGTTC
  &gt;32-24116
  TAGCATATCGAGCCTGAGAACA
  &gt;42-16312
  TGATACGGATGTTATACGCAGC
  </code></pre>
  
  <p>out: </p>
  
  <pre><code>&gt;1-242
  AGGTTCCGGATAAGTAAGAGCC
  &gt;18-41148
  TCTTAACCCGGACCAGAAACTA
  &gt;43-16054
  GTCCCACTCCGTAGATCTGTTC
  &gt;32-24116
  TAGCATATCGAGCCTGAGAACA
  &gt;42-16312
  TGATACGGATGTTATACGCAGC
  </code></pre>