[Labels] Change ordering of usa-label--{state} classes so they take precedence

[sawyerh]

Description

• Changed the ordering of the "state" classes for usa-label. This address an issue I ran into where the usa-label--error class wasn't removing the top margin that's added by the usa-label class, even though usa-label--error included margin-top: 0 in its declaration. This seemed due to the ordering of those styles.
• Removed a redundant display: block property from usa-label--error, which is already applied with the default usa-label class.

Additional information

Before you hit Submit, make sure you’ve done whichever of these applies to you:

• Follow the 18F Front End Coding Style Guide and Accessibility Guide.
• Run npm test and make sure the tests for the files you have changed have passed.
• Run your code through HTML_CodeSniffer and make sure it’s error free.
• Title your pull request using this format: [Website] - [UI component]: Brief statement describing what this pull request solves.

[mejiaj]

LGTM