[php-maint] Bug#861855: php7.0-fpm: Uses kill without depending on procps

[Adrian Heine]

Package: php7.0-fpm
Version: 7.0.16-3
Severity: serious
Justification: Policy 3.5

/lib/systemd/system/php7.0-fpm.service contains:
```
ExecReload=/bin/kill -USR2 $MAINPID
```
procps is not Essential.