Electronic storage overhaul migration fix

[ShnitzelX2]

Summary

Bugfixes "electronic storage overhaul migration fix"

Purpose of change

Closes #79299

When I wrote the migration code for #79097, evidently I removed some code that was still being used.

Describe the solution

Put the MOD reading code back for migration, ignore CONTAINER for migration.

Describe alternatives you've considered

Testing

Tested with the save from #79299, mods were back on guns, no additional errors.

Additional context

I really should have asked before I changed this code in the first place. It looks like it was to migrate contents for when pockets were introduced, but I don't know how much of it still really needs to be there.

I guess I'm asking for a second opinion if anybody knows better.

[ShnitzelX2]

My branch had issues, so I rebased and tested every pocket type with a pre-#79097 save, along with the save from #79299.

I solely re-added the mod migration code, no errors, everything where it should be.