logd: remove SocketClient from LogBuffer and LogBufferElement

In the future, we'll want to be able to write to outputs that are not
necessarily a libsysutils SocketClient, for example host tests of
LogBuffer.  Therefore, we add a LogWriter class to be used instead of
SocketClient.

Test: logging unit tests
Change-Id: I4385be65e14e83a635691a7ba79e9bf060e49484
diff --git a/logd/main.cpp b/logd/main.cpp
index 6e1144b..dfbad31 100644
--- a/logd/main.cpp
+++ b/logd/main.cpp
@@ -53,6 +53,7 @@
 #include "LogBuffer.h"
 #include "LogKlog.h"
 #include "LogListener.h"
+#include "LogReader.h"
 #include "LogStatistics.h"
 #include "LogTags.h"
 #include "LogUtils.h"