Don't create anonymous namespace

Don't create anonymous namespace separately, use the first namespace
that is created for app classloader as the anonymous namespace.

Note that the anonymous namespace is set via the new
ANDROID_NAMESPACE_TYPE_ALSO_USED_AS_ANONYMOUS. I didn't creat a new
function like android_set_anonymous_namespace as it requires uprev of
the libnativebridge interface and makes it harder to delete the old
android_init_anonymous_namespace as we have to keep it until all
proprietary bridged loaders are updated.

Bug: 130388701
Test: CtsBionicTestCases
Test: run games on http://www.monogame.net/showcase/?Android
Change-Id: I0fdd614365eaa56c4ab47538bf3772d94bd9ae55