Properly delete the persistentlogin cookie

[XhmikosR]

The previous solution did not delete the cookie.

Signed-off-by: XhmikosR xhmikosr@gmail.com

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Refs #1256 (comment)

So, in v5.0, logging out still leaves a cookie. This patch fixes this, but maybe we should be stricter with the cookie path also?

This is after logging out with v5.0:

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pi-hole-5-1-released/35577/1