JP-2928: Update NIRISS AMI3 regtest with flight data

[hbushouse]

Partially resolves JP-2928

This PR updates the test_niriss_ami3 regtest module to use recent in-flight data as input. Note that the test_ami_average_with_sizes test is no longer needed, because the one main test now also covers the case where dithering of the target and/or psf source(s) leads to outputs of different sizes that need to be averaged. All new input and truth files have been uploaded to artifactory and the new tests pass when run locally.

Checklist for maintainers

• added entry in CHANGES.rst within the relevant release section
• updated or added relevant tests
• updated relevant documentation
• added relevant milestone
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below.
  How to run regression tests on a PR
• Make sure the JIRA ticket is resolved properly

[codecov]

Codecov Report

Base: 78.60% // Head: 78.60% // No change to project coverage 👍

Coverage data is based on head (6760b8b) compared to base (e2284d1).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7434   +/-   ##
=======================================
  Coverage   78.60%   78.60%           
=======================================
  Files         455      455           
  Lines       39148    39148           
=======================================
  Hits        30771    30771           
  Misses       8377     8377           

Flag	Coverage Δ		*Carryforward flag
nightly	78.59% <ø> (ø)		Carriedforward from e2284d1
unit	51.41% <ø> (ø)

*This pull request uses carry forward flags. Click here to find out more.

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[dmggh]

Looks good to me.