logd: remove start filtration from flushTo (part deux)

We have already searched for the start point, the start filter check
is paranoia that removes out-of-order entries that we are undoubtably
interested in.  Out-of-order entries occur under reader pressure, as
the writer gets pushed back from in-place sorted order and lands it
at the end for the reader to pick it up.  If this occurred during a
batch run or a logger thread wakeup, the entry could be filtered out
and never output to the reader.

We have to treat exact finds for start in the list as terminal when
we search as they represent restarts, depending on the fact that it
is impossible to have the exact same time reported in two log entries
or requested from a batched reader.  This does break down if a log
entry has xxxxxx000 nanoseconds reported, we fix that by making sure
we never log such a case and slip it by a ns.

Found one case where logcat.tail_time* tests failed which was fixed
with this adjustment.

Test: gTest logd-unit-tests, liblog-unit-tests and logcat-unit-tests
Bug: 38046067
Bug: 37791296
Bug: 38341453
Change-Id: I4dd2e2596dd67b8d602160dd79661e01805227a9