Move JUnit classes from here into external/junit

Checked that android.test.runner had the same classes in as
before the change.

These classes are legacy 3.8.1 classes, they are not in 4.10 at
all. They appear to have been left here by accident. Looking at
the history it appears that at one time there were copies of
JUnit 3.8.1 junit.runner classes in frameworks and
external/junit. The classes here were upgraded to 4.10 but even
though these classes had been deleted immediately after 3.8.2
was released they were not removed, instead they appear to have
been reformatted as part of the upgrade. The external/junit
source was upgraded to 4.10 about two weeks later which seems to
have been done correctly. About three months after that the
classes here that were duplicates of those in external/junit
were removed from here leaving the legacy classes from 3.8.1.

I could not find any usages of these classes and they are not in
the public API so they can probably be removed altogether.
However, for now I will simply move them into external/junit as
described and remove them when upgrading JUnit there to 4.12.

Bug: 30188076
Test: Built android.test.runner and checkapi
Change-Id: I88687889315c041d999fe7e61b9652ac8406165c