Drop ro.debuggable restriction for NATIVELOADER_DEFAULT_NAMESPACE_LIBS.

To allow running tests on user builds. The (non)existence of the
environment variable itself serves fine as a toggle, and it is hard to
inject into the zygote environment on a user build anyway.

Also a few other cleanups from comments on
https://r.android.com/1689792.

Test: art/test/testrunner/testrunner.py --target --64 --optimizing
Bug: 130340935
Change-Id: I1843a8bbfb5dadc560919022d1f2123eb652be5a
2 files changed