Remove the monotonic option for logging

This has been around for ~5 years but there has been roughly no
adoption, so remove this as we clean up the logging code.

Future efforts may track the monotonic timestamp in all cases.

Test: logging unit tests
Change-Id: I55ed565669f923988e741f6b384141bba893630d
diff --git a/liblog/pmsg_writer.cpp b/liblog/pmsg_writer.cpp
index 0751e2c..8e676bd 100644
--- a/liblog/pmsg_writer.cpp
+++ b/liblog/pmsg_writer.cpp
@@ -188,7 +188,7 @@
     return -EINVAL;
   }
 
-  clock_gettime(android_log_clockid(), &ts);
+  clock_gettime(CLOCK_REALTIME, &ts);
 
   cp = strdup(filename);
   if (!cp) {