Cleanup kotlin sources

1. remove unused import
2. remove redundant semicolon
3. remove redundant empty constructor and SAM-constructor
4. remove unnecessary type argument
5. adjust indent

See gh-31913

integration-tests/src/test/kotlin/org/springframework/aop/framework/autoproxy/AspectJAutoProxyInterceptorKotlinIntegrationTests.kt

@@ -94,12 +94,12 @@ class AspectJAutoProxyInterceptorKotlinIntegrationTests(
     open class Echo {
 
         open fun echo(value: String): String {
-            return value;
+            return value
         }
 
         open suspend fun suspendingEcho(value: String): String {
             delay(1)
-            return value;
+            return value
         }
 
     }