chore: replace nyc configurations with c8 configurations

[faustbrian]

c8 supports reading the old nyc configurations but it makes more sense to rename them to the names that c8 itself uses.

[codecov]

Codecov Report

Merging #2192 (669d40f) into master (f0516de) will not change coverage.
The diff coverage is n/a.

Flag	Coverage Δ
block	93.07% <ø> (ø)
blockchain	88.82% <ø> (ø)
client	86.70% <ø> (ø)
common	98.09% <ø> (ø)
devp2p	92.25% <ø> (ø)
ethash	∅ <ø> (∅)
evm	79.07% <ø> (ø)
statemanager	88.71% <ø> (ø)
trie	89.26% <ø> (ø)
tx	97.98% <ø> (ø)
util	93.14% <ø> (ø)
vm	85.27% <ø> (ø)

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[holgerd77]

LGTM, small nit: might have been nice to use git mv for renaming to preserve the file history, but I guess in the cases of these super small configuration files this is not absolutely necessary.