do not send cancel message to peer that sent block

[gammazero]

The serving peer cleans the client's wantlint after serving the block, making sending CANCEL to the serving peer redundant. So, exclude the serving peer when sending cancels after receiving a block.

Closes #694

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.50%. Comparing base (1097a4b) to head (5d46316).

@@            Coverage Diff             @@
##             main     #784      +/-   ##
==========================================
- Coverage   60.51%   60.50%   -0.02%     
==========================================
  Files         245      245              
  Lines       31133    31134       +1     
==========================================
- Hits        18841    18837       -4     
- Misses      10615    10619       +4     
- Partials     1677     1678       +1     

Files with missing lines	Coverage Δ
bitswap/client/internal/peermanager/peermanager.go	91.85% <100.00%> (ø)
...wap/client/internal/peermanager/peerwantmanager.go	88.54% <100.00%> (+0.03%)	⬆️
bitswap/client/internal/session/session.go	90.18% <ø> (ø)
...p/client/internal/sessionmanager/sessionmanager.go	94.73% <100.00%> (-1.06%)	⬇️

... and 7 files with indirect coverage changes