Also, removes the workaround that allowed preparers to override files
added in javaMockFS().
The performance of the java tests was determined by running:
m nothing
rm -fr out/soong/.bootstrap/soong-java/test/
time m nothing
Prior to starting this work that returned:
real 1m30.060s
user 33m3.028s
sys 13m25.413s
Immediately prior to this change that returned:
real 1m2.777s
user 14m14.352s
sys 9m40.745s
After applying this change that returned:
real 0m20.282s
user 3m7.429s
sys 0m43.601s
So, this reduced the real time cost of running the java tests from 90
seconds to 20 seconds.
Bug: 182638834
Test: m nothing
Change-Id: I30490fd40ddb0684a5a4975ce1811bab5dc79e4e