Description:
------------
"FPM_SOCKETS_X" env variable isn't cleaned when it's become unused.
The issue is appeared if count of sockets is changed from "FPM_ENV_SOCKET_SET_SIZE * n + 1" to "FPM_ENV_SOCKET_SET_SIZE * n"
In such cases the same socket presents in "FPM_SOCKETS_[socket_set_count - 1]" and "FPM_SOCKETS_[socket_set_count]"
       

Test script:
---------------
#!/bin/bash -xe

# all paths are specific to default ones in Ubuntu 20.04
pool_d="/etc/php/7.4/fpm/pool.d"
pool_0="$pool_d/www.conf"
sed -i "s/^pm = dynamic$/pm = ondemand/" "$pool_0"
for i in {1001..1128}; do
    pool_i="$pool_d/www_$i.conf"
    cp -p "$pool_0" "$pool_i"
    sed -i "s/^\[www\]$/\[www_$i\]/" "$pool_i"
    sed -i "s|^listen = /run/php/php7.4-fpm.sock$|listen = /run/php/php7.4-fpm.$i.sock|" "$pool_i"
done
systemctl restart php7.4-fpm

rm -f "$pool_d/www_1001.conf"
systemctl reload php7.4-fpm
systemctl reload php7.4-fpm

Expected result:
----------------
php-fpm reloads successfully.

Actual result:
--------------
"503 Service Unavailable" is shown

```
ls: cannot access '/run/php/php7.4-fpm.1128.sock': No such file or directory
```

```
[27-Aug-2020 10:31:00] NOTICE: reloading: execvp("/usr/sbin/php-fpm7.4", {"/usr/sbin/php-fpm7.4", "--nodaemonize", "--fpm-config", "/etc/php/7.4/fpm/php-fpm.conf"})
[27-Aug-2020 10:31:02] NOTICE: using inherited socket fd=7, "/run/php/php7.4-fpm.sock"
[27-Aug-2020 10:31:02] NOTICE: using inherited socket fd=135, "/run/php/php7.4-fpm.1128.sock"
[27-Aug-2020 10:31:02] NOTICE: using inherited socket fd=9, "/run/php/php7.4-fpm.1002.sock"
...
[27-Aug-2020 10:31:02] NOTICE: using inherited socket fd=134, "/run/php/php7.4-fpm.1127.sock"
[27-Aug-2020 10:31:02] NOTICE: using inherited socket fd=135, "/run/php/php7.4-fpm.1128.sock"
[27-Aug-2020 10:31:02] ERROR: epoll: unable to add fd 135
```