removes pubkey references

[behzadnouri]

Problem

The pubkeys are retained until the next epoch:
https://github.com/solana-labs/solana/blob/8376781ec/core/src/replay_stage.rs#L1867-L1869
plus the overhead of Rc itself.
So not clear these are saving any memory over the plain pubkeys.
And they are not necessary for the code logic either,
but they have a negative impact on the runtime.

Summary of Changes

Removed PubkeyReferences

[behzadnouri]

Left chunk is after removing the pubkey references:

replay-loop-timing-stats::compute_bank_stats_elapsed:

[codecov]

Codecov Report

Merging #15050 (d89a5aa) into master (8376781) will decrease coverage by 0.0%.
The diff coverage is 73.9%.

@@            Coverage Diff            @@
##           master   #15050     +/-   ##
=========================================
- Coverage    79.6%    79.6%   -0.1%     
=========================================
  Files         401      401             
  Lines      101108   101058     -50     
=========================================
- Hits        80524    80468     -56     
- Misses      20584    20590      +6     

[carllin]

Thanks for the cleanup! Can also probably be removed from cluster_info_vote_listener and cluster_slots.rs

[behzadnouri]

Thanks for the cleanup! Can also probably be removed from cluster_info_vote_listener and cluster_slots.rs

yes, I will send you another pull request for that