`failOnWarning` must be turned ON in eo-runtime

[yegor256]

Currently, failOnWarning is set to false in eo-runtime/pom.xml. Let's put it to true and fix all warnings in .eo files: most of them are cosmetic.

[iri]

I will take this.

[yegor256]

@iri great! please, don't do it in one big pull request, to avoid risk of rejection.

[uchitsa]

@yegor256 I'm already started work on it and added some fixes. Please check PR #3692