8010268: Remove dependence upon clean target from jdk/test/Makefile prep target

Reviewed-by: tbell, mchung
diff --git a/jdk/test/Makefile b/jdk/test/Makefile
index 2b4bfa1..676d6bc 100644
--- a/jdk/test/Makefile
+++ b/jdk/test/Makefile
@@ -336,7 +336,7 @@
 	@$(ECHO) "Testing completed successfully"
 
 # Prep for output
-prep: clean
+prep:
 	@$(MKDIR) -p $(ABS_TEST_OUTPUT_DIR)
 	@$(MKDIR) -p `$(DIRNAME) $(ARCHIVE_BUNDLE)`