MB-46604: Use folly executor for phosphor tracing [6/6]

Remove the homegrown executor service and use the folly
CPU executor for formatting the phosphor trace dumps.

This patch temporarily disables the automatic purging of old
trace dumps, but manually trigger a check every time one
tries to request one.

The automatic purge will be added after we've promoted the
executor service from ep-engine to the core.

Change-Id: I4a9062f4f6c921222ce1312ce8df4f1f09649c27
Reviewed-on: http://review.couchbase.org/c/kv_engine/+/154645
Tested-by: Build Bot <build@couchbase.com>
Reviewed-by: Dave Rigby <daver@couchbase.com>

daemon/CMakeLists.txt

@@ -30,10 +30,6 @@ add_library(memcached_daemon STATIC
             enginemap.cc
             enginemap.h
             environment.cc
-            executor.cc
-            executor.h
-            executorpool.cc
-            executorpool.h
             front_end_thread.h
             get_authorization_task.cc
             get_authorization_task.h
@@ -174,8 +170,6 @@ add_library(memcached_daemon STATIC
             subdocument_traits.h
             subdocument_validators.cc
             subdocument_validators.h
-            task.h
-            task.cc
             thread.cc
             timing_histogram.cc
             timing_histogram.h
@@ -186,8 +180,7 @@ add_library(memcached_daemon STATIC
             topkeys.cc
             topkeys.h
             tracing.cc
-            tracing.h
-            tracing_types.h)
+            tracing.h)
 
 if (NUMA_FOUND)
     target_include_directories(memcached_daemon