Remove tools/code_check and update codecov

[chapulina]

See gazebo-tooling/action-gz-ci#32 and gazebo-tooling/release-tools#446

[codecov]

Codecov Report

Merging #814 (af206f1) into ign-gazebo3 (01fc2ff) will increase coverage by 12.14%.
The diff coverage is 90.82%.

❗ Current head af206f1 differs from pull request most recent head fb93200. Consider uploading reports for the commit fb93200 to get more accurate results

@@               Coverage Diff                @@
##           ign-gazebo3     #814       +/-   ##
================================================
+ Coverage        65.71%   77.85%   +12.14%     
================================================
  Files              127      216       +89     
  Lines             6238    12150     +5912     
================================================
+ Hits              4099     9459     +5360     
- Misses            2139     2691      +552     

Impacted Files	Coverage Δ
include/ignition/gazebo/EntityComponentManager.hh	100.00% <ø> (ø)
include/ignition/gazebo/Link.hh	100.00% <ø> (ø)
include/ignition/gazebo/Model.hh	100.00% <ø> (ø)
include/ignition/gazebo/SdfEntityCreator.hh	100.00% <ø> (ø)
include/ignition/gazebo/Server.hh	100.00% <ø> (ø)
include/ignition/gazebo/ServerConfig.hh	100.00% <ø> (ø)
include/ignition/gazebo/System.hh	100.00% <ø> (ø)
include/ignition/gazebo/components/Component.hh	100.00% <ø> (ø)
include/ignition/gazebo/gui/GuiEvents.hh	0.00% <0.00%> (ø)
src/SimulationRunner.hh	100.00% <ø> (ø)
... and 200 more

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[chapulina]

It's not often that we see 12 🟢 on ign-gazebo 😄