Fix dex file leak in oat file manager

Simplified ownership by having a vector of unique pointers own
all newly opened dex files.

Bug: 29246280

(cherry picked from commit fed316715faeec7bf34e3c4a878288c1342cb0e8)

Change-Id: I97db09ced76db8ffdbae371ff72977c4276a0494
1 file changed