Fix redir_to_coach after 2023/07 coach reform

[dominiquelee]

This fixes #1706.

• Fix redir_to_coach (open specialist page)

The recent coach reform changed the Hattrick-generated link from the player page to the specialist page. The player page barely contain any information about the coach status (salary + link to specialist page), so there is no point in opening it.

Trying to redirect to a null URL is a no-op operation, so in case of error, we would only open the Players page.

• In redir_to_coach, remove NT coach redirection code

This feature has been removed from Hattrick for a few years at this point.

[minj]

Thanks

[dominiquelee]

Oops, I messed up, I didn't parse the URL to make it relative. This PR is broken and doesn't fix anything.