Remove fallback because peer will only send TWCC

[mengelbart]

The peer negotiated TWCC so this is what is will send us. Falling back to sequence numbers doesn't help here because we won't be able to match the numbers to the incoming TWCC reports. We only push items to the history that will never be used.

Also reduce the logging by logging the warning once instead of repeating it for every packet.

[codecov]

Codecov Report

❌ Patch coverage is 12.50000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.35%. Comparing base (0e9d5ea) to head (2c2a1a3).

Files with missing lines	Patch %	Lines
pkg/rtpfb/interceptor.go	12.50%	7 Missing ⚠️

❌ Your patch check has failed because the patch coverage (12.50%) is below the target coverage (70.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #448      +/-   ##
==========================================
+ Coverage   81.32%   81.35%   +0.02%     
==========================================
  Files          88       88              
  Lines        4649     4651       +2     
==========================================
+ Hits         3781     3784       +3     
  Misses        689      689              
+ Partials      179      178       -1     

Flag	Coverage Δ
go	81.35% <12.50%> (+0.02%)	⬆️

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