Update PGO configuration

Bug: http://b/63768402

- Remove the 'enable_profile_use' property.  This is a no-op change with
https://android-review.googlesource.com/c/591562 - PGO profile use is
only enabled if the profile file exists.  We don't have one yet.
- Move the profile file location to an art/ subdirectory so it doesn't
conflict with profiles for other projects

Test: Build AOSP
Change-Id: Ifb7cded58a786dc5b1024a4c2c770873fcf4413c