remove generated java directory under ./out before tasty test

Author: liufengyun

test/dotc/tests.scala

@@ -288,8 +288,9 @@ class tests extends CompilerTest {
   @Test def tasty_tests = compileDir(testsDir, "tasty", testPickling)
 
   @Test def tasty_bootstrap = {
-    // remove class files from stdlib compilation
+    // remove class files from stdlib and tests compilation
     Directory(defaultOutputDir + "scala").deleteRecursively()
+    Directory(defaultOutputDir + "java").deleteRecursively()
 
     val opt = List("-classpath", defaultOutputDir, "-Ylog-classpath")
     // first compile dotty