Proto: remove tmp_to_old_committee and tmp_of_old_committee

Fixes #7935 (closed)

There is only one remaining mention of #7935 (closed), but it is in the tests and tracked in Milestone %(2025Q2) AQEAB - Aggregation with DAL slots, so it can be addressed later.

grep -r "issues\/7935" src/proto_alpha/*
src/proto_alpha/lib_protocol/test/integration/consensus/test_aggregate.ml:      
      (* TODO: https://gitlab.com/tezos/tezos/-/issues/7935
         Add tests with dal_content = Some _. *)

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
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