Temporarily remove codecov CI check

[cmichi]

• There is some strange linker error in the master CI.
• We can't reproduce it locally.
• We suspect that it might have to do with an outdated docker image.
• The failing master CI blocks publishing a new ink-ci-linux:production image.
• The codecov check is broken since a few days anyway (due to some token issue). I created this ticket at the time: https://github.com/paritytech/ci_cd/issues/160.
• We can bring the check back as soon as we sorted the linker error out in a PR.

[HCastano]

We suspect that it might have to do with an outdated docker image.

I was testing out the Docker images locally and I haven't found this to be the case. Running:

# On host machine
sudo docker run -it paritytech/ink-ci-linux:production

# In Docker container
git clone https://github.com/paritytech/ink/
cd ink && cargo test --verbose --all-features --no-fail-fast --workspace

Works just fine.

I'm thinking it's either something to do with the RUSTFLAGS, or maybe come caching issues on the runners.

Either way, Codecov is clearly broken right now, so yeah let's get this merged.