Drizzlepac/HAP: Fix poller_utils so it works properly with a list for MVM processing

[stscijgbot-hstdp]

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Issue HLA-779 was created on JIRA by Michele De La Pena Extesnsion 9/19/25 [X]:

The poller_utils.py module is supposed to accept both true {}poller file{}, as generated by operational databases, or an ascii file containing a list of SVM FLT/FLC images to use as input for MVM processing.  However, it looks as though the build_poller_table function is still expecting the list input for MVM processing to be the pipeline FLT/FLC files and not the SVM FLT/FLC files.

This needs to be checked to see if is still or actually was a problem.