Use default Kotlin plugin settings

Rather than override the default, this commit removes the override for
the incremental compilation support in Maven. We now relies on all
default now.

Closes gh-584

initializr-generator/src/test/resources/project/maven/kotlin-java9-pom.xml.gen

@@ -19,7 +19,6 @@
 	</parent>
 
 	<properties>
-		<kotlin.compiler.incremental>true</kotlin.compiler.incremental>
 		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
 		<java.version>9</java.version>