[BF] remove incorrect '/admin' from URLROOT

[listerr]

Was getting set twice and requesting "/admin/admin...."

URL_LOCK="${URLROOT}/admin/api/v4/router/get-update-lock"
URL_CONF="${URLROOT}/admin/api/v4/router/gen-config"
URL_RELEASE="${URLROOT}/admin/api/v4/router/release-update-lock"
URL_DONE="${URLROOT}/admin/api/v4/router/updated"

PR template - remove this line and edit below

[BF] Summary of fix - fixes [inex|islandbridgenetworks]/IXP-Manager#x

[NF] New feature summary - closes [inex|islandbridgenetworks]/IXP-Manager#x

Longer description

In addition to the above, I have:

• ensured unit tests all run without error
• ran psalm and corrected any static analysis issues
• ensured all relevant template output is escaped to avoid XSS attached with <?= $t->ee( $data ) ?> or equivalent
• ensured appropriate checks against user privilege / resources accessed
• API calls (particular for add/edit/delete/toggle) are not implemented with GET and use CSRF tokens to avoid CSRF attacks