chore: drop unused update_wallet_balance from WalletManager

[xdustinface]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.13%. Comparing base (d5bec1e) to head (8bab1cc).
⚠️ Report is 3 commits behind head on v0.42-dev.

Additional details and impacted files

@@              Coverage Diff              @@
##           v0.42-dev     #560      +/-   ##
=============================================
- Coverage      66.13%   66.13%   -0.01%     
=============================================
  Files            311      311              
  Lines          64757    64751       -6     
=============================================
- Hits           42829    42824       -5     
+ Misses         21928    21927       -1     

Flag	Coverage Δ
core	75.13% <ø> (ø)
ffi	37.12% <ø> (-0.02%)	⬇️
rpc	28.28% <ø> (ø)
spv	80.78% <ø> (-0.03%)	⬇️
wallet	65.52% <ø> (+0.02%)	⬆️

Files with missing lines	Coverage Δ
key-wallet-manager/src/wallet_manager/mod.rs	48.40% <ø> (+0.48%)	⬆️

... and 2 files with indirect coverage changes