Remove all cleverness that broke uploads

[9seconds]

This fixes #233

I have removed syncPairs and fancy tricks that bufferize writes simulating TCP_CORK. They allow to achieve better performance but break uploads. This was unexpected but it seems that this part of the protocol is quite sensitive to timings. This hotfix PR removes a cleverness

[codecov-commenter]

Codecov Report

Merging #234 (93bed24) into master (219235e) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #234      +/-   ##
==========================================
+ Coverage   82.56%   82.60%   +0.04%     
==========================================
  Files          69       68       -1     
  Lines        1927     1897      -30     
==========================================
- Hits         1591     1567      -24     
+ Misses        236      232       -4     
+ Partials      100       98       -2     

Impacted Files	Coverage Δ
mtglib/internal/relay/pools.go	100.00% <100.00%> (ø)
mtglib/internal/relay/relay.go	92.85% <100.00%> (-0.48%)	⬇️

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