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/logger_write.cpp b/liblog/logger_write.cpp
index 3a75fa3..22c7eca 100644
--- a/liblog/logger_write.cpp
+++ b/liblog/logger_write.cpp
@@ -192,7 +192,7 @@
     return -EINVAL;
   }
 
-  clock_gettime(android_log_clockid(), &ts);
+  clock_gettime(CLOCK_REALTIME, &ts);
 
   if (log_id == LOG_ID_SECURITY) {
     if (vec[0].iov_len < 4) {