Remove Commit gossiping logic from P2P client

[Manav-Aggarwal]

Since SignedHeaders are gossiped, there is no use for Commit gossiping. Entire related logic should be removed from p2p.Client and node(s).

Closes: #686

[codecov-commenter]

Codecov Report

Base: 55.07% // Head: 55.24% // Increases project coverage by +0.17% 🎉

Coverage data is based on head (d2ad8f6) compared to base (a1643e1).
Patch coverage: 100.00% of modified lines in pull request are covered.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #717      +/-   ##
==========================================
+ Coverage   55.07%   55.24%   +0.17%     
==========================================
  Files          52       52              
  Lines        9851     9814      -37     
==========================================
- Hits         5425     5422       -3     
+ Misses       3618     3590      -28     
+ Partials      808      802       -6     

Impacted Files	Coverage Δ
node/full.go	61.96% <ø> (+3.63%)	⬆️
p2p/client.go	60.43% <ø> (-0.30%)	⬇️
block/manager.go	64.31% <100.00%> (+0.51%)	⬆️
state/executor.go	65.54% <0.00%> (+0.72%)	⬆️
types/validation.go	51.16% <0.00%> (+13.95%)	⬆️

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[tzdybal]

LGTM