adb: clean up debug tracing a little.

Always use LOG() for debug tracing.
Remove useless D_lock. I believe it is useless to lock just before and after fprintf.

I verified the log output both on host and on device. The output looks fine to me.

Change-Id: I96ccfe408ff56864361551afe9ad464d197ae104
diff --git a/adb/client/main.cpp b/adb/client/main.cpp
index 8d644d9..6e27c0f 100644
--- a/adb/client/main.cpp
+++ b/adb/client/main.cpp
@@ -163,7 +163,7 @@
 #endif
     }
 
-    D("Event loop starting\n");
+    D("Event loop starting");
     fdevent_loop();
 
     return 0;