Remove unused import.

Author: joewyz

smithy-trait-codegen/src/main/java/software/amazon/smithy/traitcodegen/writer/TraitCodegenWriter.java

@@ -20,7 +20,6 @@
 import software.amazon.smithy.traitcodegen.TraitCodegenSettings;
 import software.amazon.smithy.traitcodegen.TraitCodegenUtils;
 import software.amazon.smithy.utils.ListUtils;
-import software.amazon.smithy.utils.SetUtils;
 import software.amazon.smithy.utils.StringUtils;
 
 /**