Remove want-block sent tracking from sessionWantSender

[gammazero]

Tracking want-blocks that were sent to a peer is not necessary to do in sessionwantsender. This is already handled in peermanager/peerwantmanager.

Removing this tracking reduces unnecessary memory use.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.40%. Comparing base (3cee549) to head (a7f6755).

@@            Coverage Diff             @@
##             main     #759      +/-   ##
==========================================
- Coverage   60.46%   60.40%   -0.07%     
==========================================
  Files         245      244       -1     
  Lines       31126    31094      -32     
==========================================
- Hits        18821    18782      -39     
- Misses      10629    10634       +5     
- Partials     1676     1678       +2     

Files with missing lines	Coverage Δ
...tswap/client/internal/session/sessionwantsender.go	97.56% <100.00%> (+0.61%)	⬆️

... and 14 files with indirect coverage changes