chore(codegen): Remove unnecessary println of start of codegen (#497)

Author: kggilmer

smithy-kotlin-codegen/src/main/kotlin/software/amazon/smithy/kotlin/codegen/KotlinCodegenPlugin.kt

@@ -17,10 +17,7 @@ import software.amazon.smithy.model.Model
 class KotlinCodegenPlugin : SmithyBuildPlugin {
     override fun getName(): String = "kotlin-codegen"
 
-    override fun execute(context: PluginContext?) {
-        println("executing kotlin codegen")
-        CodegenVisitor(context!!).execute()
-    }
+    override fun execute(context: PluginContext?) = CodegenVisitor(context ?: error("context was null")).execute()
 
     companion object {
         /**