Cleanup old headers and namespace declarations

Remove the header includes for the old phosphor::logging::log API
as well as unnecessary phosphor::logging namespace declarations.
Fully qualify phosphor::logging namespace where applicable and/or
needed.

Tested:
* Verified commit passed CI unit tests.
* Verified commit built using bitbake.

Change-Id: I2e490e1aa3fd3423f8c52694c2b97bc58b95525a
Signed-off-by: Anwaar Hadi <anwaar.hadi@ibm.com>
diff --git a/monitor/tach_sensor.cpp b/monitor/tach_sensor.cpp
index 5790bab..cce3139 100644
--- a/monitor/tach_sensor.cpp
+++ b/monitor/tach_sensor.cpp
@@ -343,7 +343,7 @@
             // Log an internal error for undefined timer mode
             lg2::error("Undefined timer mode: {TIMER_MODE}", "TIMER_MODE",
                        mode);
-            elog<InternalFailure>();
+            phosphor::logging::elog<InternalFailure>();
             return duration_cast<microseconds>(seconds(0));
     }
 }