chore: remove rinkeby and kovan

[tmigone]

With Etherscan deprecating Rinkeby/Kovan block explorers support for the old testnets is pretty much gone.

Signed-off-by: Tomás Migone tomas@edgeandnode.com

[codecov]

Codecov Report

Base: 90.57% // Head: 90.57% // No change to project coverage 👍

Coverage data is based on head (97dcb77) compared to base (04cfd3a).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #729   +/-   ##
=======================================
  Coverage   90.57%   90.57%           
=======================================
  Files          35       35           
  Lines        1762     1762           
  Branches      296      296           
=======================================
  Hits         1596     1596           
  Misses        166      166           

Flag	Coverage Δ
unittests	90.57% <ø> (ø)

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