Make certain `./lib` doesn't require goja

[mstoykov]

./lib should not depend on goja. I thought we fixed that with the metrics and thresholds rewrite but it turns out we did add one more dependency a year ago in the form of https://github.com/grafana/k6/blob/5c357289fcc7a717a9b39990bd975ea2784b42bc/lib/executor/helpers.go#L128 and then another one around the grpc refactor https://github.com/grafana/k6/blob/5c357289fcc7a717a9b39990bd975ea2784b42bc/lib/netext/grpcext/conn.go#L58

Both of those should be removed and we should probably figure out some way to make certain we don't import the js package from lib and ... other places

[codebien]

It could be helpful to implement https://github.com/OpenPeeDeeP/depguard or something similar to avoid the same mistake in the future.

[na--]

Closed by https://github.com/grafana/k6/pull/2809 (which was actually merged in https://github.com/grafana/k6/pull/2826)