Remove unneeded exception in memory.py

[gaborszita]

Closes #460

The call to as_wires is needed in _assignment, tests fail without that.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.9%. Comparing base (5077c24) to head (3b1c7d4).
Report is 9 commits behind head on development.

Additional details and impacted files

@@              Coverage Diff              @@
##           development    #463     +/-   ##
=============================================
+ Coverage         91.7%   91.9%   +0.3%     
=============================================
  Files               24      24             
  Lines             6403    6410      +7     
=============================================
+ Hits              5866    5886     +20     
+ Misses             537     524     -13     

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