Add test where unused file is removed

jps-plugin/testData/incremental/pureKotlin/removeUnusedFile/build.log

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+================ Step #1 =================
+
+Cleaning output files:
+  out/production/module/META-INF/module.kotlin_module
+  out/production/module/test/Bar.class
+  out/production/module/test/UnusedKt.class
+End of files
+Compiling files:
+End of files
+Exit code: OK
+------------------------------------------

jps-plugin/testData/incremental/pureKotlin/removeUnusedFile/dummy.kt

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+package test
+
+fun dummy() {}

jps-plugin/testData/incremental/pureKotlin/removeUnusedFile/unused.kt

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+package test
+
+fun foo() {}
+
+class Bar() {}