cleanup checkstyle warnings

This change:

1. Separate checkstyle config for tests that is a bit more relaxed. In particular, no javadoc requirements or magic number check.
2. Removed unused nflx_checks.xml file.
3. Cleanup some misc formatting issues that were causing warnings.

Checkstyle now runs cleanly:

$ ./gradlew checkstyleTest
:servo-core:compileJava UP-TO-DATE
:servo-core:processResources UP-TO-DATE
:servo-core:classes UP-TO-DATE
:servo-core:jar UP-TO-DATE
:servo-aws:compileJava UP-TO-DATE
:servo-aws:processResources UP-TO-DATE
:servo-aws:classes UP-TO-DATE
:servo-aws:compileTestJava UP-TO-DATE
:servo-aws:processTestResources UP-TO-DATE
:servo-aws:testClasses UP-TO-DATE
:servo-aws:checkstyleTest UP-TO-DATE
:servo-core:compileTestJava UP-TO-DATE
:servo-core:processTestResources UP-TO-DATE
:servo-core:testClasses UP-TO-DATE
:servo-core:checkstyleTest UP-TO-DATE
:servo-graphite:compileJava UP-TO-DATE
:servo-graphite:processResources UP-TO-DATE
:servo-graphite:classes UP-TO-DATE
:servo-graphite:jar UP-TO-DATE
:servo-example:compileJava UP-TO-DATE
:servo-example:processResources UP-TO-DATE
:servo-example:classes UP-TO-DATE
:servo-example:compileTestJava UP-TO-DATE
:servo-example:processTestResources UP-TO-DATE
:servo-example:testClasses UP-TO-DATE
:servo-example:checkstyleTest UP-TO-DATE
:servo-graphite:compileTestJava UP-TO-DATE
:servo-graphite:processTestResources UP-TO-DATE
:servo-graphite:testClasses UP-TO-DATE
:servo-graphite:checkstyleTest UP-TO-DATE

BUILD SUCCESSFUL

Total time: 11.384 secs