snapuserd: Run snapuserd threads in-process.

This removes the temporary daemon and socket and instead directly embeds
SnapshotHandlerManager. We can also remove the test flags for io_uring
as with this they're no longer necessary.

Bug: 269361087
Test: snapuserd_test
Ignore-AOSP-First: cherry-pick from aosp
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:269e99f9558ae332e10329451fc51dc6698375a0)
Merged-In: I728186d9bc90c98fabd76d3f86569840488ada96
Change-Id: I728186d9bc90c98fabd76d3f86569840488ada96
5 files changed