[FxImporter] remove weakref finalizer of reftracker

[egebeysel]

Fixes iree-org/iree-turbine#281.

TL;DR:

The weakref.finalize objects cause the model parameters to be kept in memory in-between consecutive aot.export calls in the same process. We remove them to enable releasing the memory, this does not change the behavior of RefTracker or RefMapping classes anyhow else.

[egebeysel]

@stellaraccident could you please review/approve and merge if everything looks alright :) Thanks!

[penguin-wwy]

Could you comment out this section of code and add the issue link in the comments instead of deleting it directly?

[stellaraccident]

Could you comment out this section of code and add the issue link in the comments instead of deleting it directly?

This is a good idea: let's do that. I think this is safe to do, but this part was complicated. Let's plan for our future selves to have some context.

If changed as requested, then this lgtm

[egebeysel]

Could you comment out this section of code and add the issue link in the comments instead of deleting it directly?

This is a good idea: let's do that. I think this is safe to do, but this part was complicated. Let's plan for our future selves to have some context.

Makes sense, updated it 👍