RFR: 8079191 remove remaining references to "cp -p" from langtools/test

[Jonathan Gibbons]

Two remaining uses of "cp -p" in the few remaining langtools shell tests.

In both cases, the files being copied are not being used in situations 
where it is important to preserve file attributes, and so it is safe to 
remove -p without affecting the test. In particular, typically the most 
important reason to use "cp -p" in a javac shell test is to preserve 
file modification times, when testing the choice between source and 
class files, and that is not the case here.

Bug: https://bugs.openjdk.java.net/browse/JDK-8079191
Review: http://cr.openjdk.java.net/~jjg/8079191/webrev.00/index.html

-- Jon