chore(internal/trie/node): remove all mutexes

[qdm12]

Changes

• Remove leaf's encodingMu since it was a temporary fix I forgot to remove in fix(trie): memory leak fix in lib/trie #2009 as far as I recall
• Remove leaf and branch rw mutex since it's not needed (all code is pretty much synchronous and called synchronously through mutexes etc.)

Tests

go test -count 1 -race ./internal/trie/... ./lib/trie/...

Issues

Done to test a comment after discussion with sigmap on Slack

Primary Reviewer

[codecov]

Codecov Report

Merging #2301 (c87c07a) into development (63303a3) will decrease coverage by 0.10%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           development    #2301      +/-   ##
===============================================
- Coverage        57.37%   57.27%   -0.11%     
===============================================
  Files              211      211              
  Lines            27759    27736      -23     
===============================================
- Hits             15927    15885      -42     
- Misses           10202    10218      +16     
- Partials          1630     1633       +3     

Flag	Coverage Δ
unit-tests	57.27% <ø> (-0.11%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
internal/trie/node/branch.go	100.00% <ø> (ø)
internal/trie/node/copy.go	100.00% <ø> (ø)
internal/trie/node/hash.go	84.21% <ø> (-1.51%)	⬇️
internal/trie/node/leaf.go	100.00% <ø> (ø)
internal/trie/node/leaf_encode.go	78.57% <ø> (-1.70%)	⬇️
lib/blocktree/node.go	65.98% <0.00%> (-6.81%)	⬇️
lib/blocktree/blocktree.go	54.87% <0.00%> (-1.09%)	⬇️
dot/network/service.go	55.88% <0.00%> (-0.91%)	⬇️
dot/network/light.go	85.25% <0.00%> (-0.80%)	⬇️
... and 1 more

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