Remove references to flowrun.parent_id which is no longer set by mailroom

[rowanseymour]

No description provided.

[codecov-commenter]

Codecov Report

Merging #57 (db981d0) into main (d245215) will increase coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #57      +/-   ##
==========================================
+ Coverage   67.83%   67.96%   +0.12%     
==========================================
  Files           6        6              
  Lines         827      824       -3     
==========================================
- Hits          561      560       -1     
+ Misses        152      151       -1     
+ Partials      114      113       -1     

Impacted Files	Coverage Δ
archives/runs.go	63.85% <ø> (+1.06%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d245215...db981d0. Read the comment docs.