Fix idempotency issues with deleting a form

[jnwatson]

No description provided.

[codecov]

Codecov Report

Merging #2112 (9c8fc1f) into master (776bfd0) will decrease coverage by 0.13%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2112      +/-   ##
==========================================
- Coverage   96.95%   96.82%   -0.14%     
==========================================
  Files         151      151              
  Lines       30222    30226       +4     
==========================================
- Hits        29303    29266      -37     
- Misses        919      960      +41     

Flag	Coverage Δ
linux	96.82% <100.00%> (-0.14%)	⬇️
linux_replay	?

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Impacted Files	Coverage Δ
synapse/cortex.py	95.92% <100.00%> (-0.67%)	⬇️
synapse/datamodel.py	94.78% <100.00%> (ø)
synapse/tests/utils.py	93.77% <0.00%> (-2.12%)	⬇️
synapse/lib/hiveauth.py	96.10% <0.00%> (-0.75%)	⬇️
synapse/lib/view.py	94.18% <0.00%> (-0.70%)	⬇️
synapse/lib/trigger.py	93.91% <0.00%> (-0.44%)	⬇️
synapse/lib/layer.py	98.28% <0.00%> (-0.06%)	⬇️

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