Fixed install/remove of telegraf on non-systemd Debian/Ubuntu systems (#2360)

scripts/pre-remove.sh

@@ -5,11 +5,10 @@ BIN_DIR=/usr/bin
 # Distribution-specific logic
 if [[ -f /etc/debian_version ]]; then
     # Debian/Ubuntu logic
-    which systemctl &>/dev/null
-    if [[ $? -eq 0 ]]; then
-	deb-systemd-invoke stop telegraf.service
+    if [[ "$(readlink /proc/1/exe)" == */systemd ]]; then
+        deb-systemd-invoke stop telegraf.service
     else
-	# Assuming sysv
-	invoke-rc.d telegraf stop
+        # Assuming sysv
+        invoke-rc.d telegraf stop
     fi
 fi