Remove call to expire_all in ODL code

[jonathangreen]

Description

Move the call to expire_all into the test code.

Motivation and Context

I noticed this while working on #2074. I was wondering if you considered this approach @dbernstein of putting this call into the tests instead of the main codebase. Generally, I think, mucking about with the session should be avoided as much as we can.

I left this in draft because I wanted to get your feedback on it @dbernstein, in case there is some pitfall here that I might be falling into.

How Has This Been Tested?

• Running unit tests

Checklist

• I have updated the documentation accordingly.
• All new and existing tests passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.79%. Comparing base (557663c) to head (79e10f8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2076   +/-   ##
=======================================
  Coverage   90.79%   90.79%           
=======================================
  Files         344      344           
  Lines       40601    40600    -1     
  Branches     8796     8796           
=======================================
  Hits        36862    36862           
+ Misses       2485     2484    -1     
  Partials     1254     1254           

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[jonathangreen]

I'm going to close this one and roll it into changes I need to make for holds in PP-1728.