fix: avoid racy memstores when estimating gas

[arajasek]

Related Issues

We've noticed some uncertainty when estimating gas with the new memstore introduced to the CallWithGas method in #8293.

Proposed Changes

We can investigate and fix later, but this PR just removes the buffered store for now.

Additional Info

Checklist

Before you mark the PR ready for review, please make sure that:

• All commits have a clear commit message.
• The PR title is in the form of of <PR type>: <area>: <change being made>
  • example: fix: mempool: Introduce a cache for valid signatures
  • PR type: fix, feat, INTERFACE BREAKING CHANGE, CONSENSUS BREAKING, build, chore, ci, docs,perf, refactor, revert, style, test
  • area: api, chain, state, vm, data transfer, market, mempool, message, block production, multisig, networking, paychan, proving, sealing, wallet, deps
• This PR has tests for new functionality or change in behaviour
• If new user-facing features are introduced, clear usage guidelines and / or documentation updates should be included in https://lotus.filecoin.io or Discussion Tutorials.
• CI is green

[codecov]

Codecov Report

Merging #8351 (4af8b8e) into master (a94e47c) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #8351      +/-   ##
==========================================
- Coverage   40.23%   40.19%   -0.04%     
==========================================
  Files         682      682              
  Lines       74428    74427       -1     
==========================================
- Hits        29946    29919      -27     
- Misses      39247    39267      +20     
- Partials     5235     5241       +6     

Impacted Files	Coverage Δ
chain/stmgr/call.go	69.02% <100.00%> (+3.07%)	⬆️
chain/actors/builtin/miner/diff.go	48.52% <0.00%> (-10.30%)	⬇️
markets/retrievaladapter/client_blockstore.go	62.50% <0.00%> (-6.25%)	⬇️
storage/wdpost_sched.go	77.45% <0.00%> (-3.93%)	⬇️
extern/storage-sealing/currentdealinfo.go	71.17% <0.00%> (-3.61%)	⬇️
chain/vm/mkactor.go	48.48% <0.00%> (-3.04%)	⬇️
chain/sub/incoming.go	45.25% <0.00%> (-2.45%)	⬇️
blockstore/buffered.go	34.44% <0.00%> (-2.23%)	⬇️
chain/events/events_called.go	83.90% <0.00%> (-1.47%)	⬇️
chain/stmgr/searchwait.go	67.30% <0.00%> (-1.29%)	⬇️
... and 11 more