logd: drop mSequence from LogBufferElement

Use getRealTime() instead and leverage private liblog log_time
comparison and math functions.  This saves 8 bytes off each
element in the logging database.

Test: gTest liblog-unit-tests logd-unit-tests logcat-unit-tests
Bug: 35373582
Change-Id: Ia55ef8b95cbb2a841ccb1dae9a24f314735b076a
diff --git a/logd/LogBuffer.h b/logd/LogBuffer.h
index 92b0297..fcf6b9a 100644
--- a/logd/LogBuffer.h
+++ b/logd/LogBuffer.h
@@ -115,7 +115,7 @@
 
     int log(log_id_t log_id, log_time realtime, uid_t uid, pid_t pid, pid_t tid,
             const char* msg, unsigned short len);
-    uint64_t flushTo(SocketClient* writer, const uint64_t start,
+    log_time flushTo(SocketClient* writer, const log_time& start,
                      bool privileged, bool security,
                      int (*filter)(const LogBufferElement* element,
                                    void* arg) = NULL,