Disable memory_tracker and file_tracker in unstask.sh properly

stop_dstat() calls stop_process() for dstat, memory_tracker and
file_tracker respectively. Inside stop_process(), a check for the
existence of the service is performed by is_service_enabled().

So even if we apply this seemingly dangerous commit,
is_service_enabled() is respected, so it's safe.

Closes-Bug: #1998990
Change-Id: Ica58cdb1d60c4c796f582d82ed2cde0be94b1a7e
Signed-off-by: Nobuhiro MIKI <nmiki@yahoo-corp.jp>

Author: bobuhiro11

unstack.sh

@@ -168,9 +168,7 @@ if is_service_enabled etcd3; then
     cleanup_etcd3
 fi
 
-if is_service_enabled dstat; then
-    stop_dstat
-fi
+stop_dstat
 
 # NOTE: Cinder automatically installs the lvm2 package, independently of the
 # enabled backends. So if Cinder is enabled, and installed successfully we are