This patch removes LocalSocketImpl.flush(). In practice this function
was simply a wrapper around `Thread.sleep(10)`. All direct calls to
this function have been removed. The `flush()` function is still called
on several objects that wrap a SocketOutputStream.
This will make booting a device 20ms faster than it currently is.
Bug: 139192244
Test: Build -> flash -> boot -> launch app
Change-Id: I0a96f4bc72461670370f61e847349f32af5ac774
9d8b926859