Chore: remove ConfigOps.normalize in favor of ConfigOps.getRuleSeverity

[not-an-aardvark]

What is the purpose of this pull request? (put an "X" next to item)

[x] Other, please explain:

What changes did you make? (Give an overview)

This removes the normalize method from config-ops in favor of a getRuleSeverity method.

Previously, ConfigOps.normalize would only convert string severities to numeric severities, but it would still leave severities in arrays, and Linter used a separate getRuleSeverity function to extract them. Now ConfigOps.getRuleSeverity handles both operations, so the getRuleSeverity function in Linter is redundant.

The goal of this change is to (a) reduce the number of places where modules mutate each others' objects, and (b) organize the rule severity logic into one place.

Is there anything you'd like reviewers to focus on?

Nothing in particular

[eslintbot]

LGTM

[mention-bot]

@not-an-aardvark, thanks for your PR! By analyzing the history of the files in this pull request, we identified @nzakas, @gyandeeps and @mysticatea to be potential reviewers.