(ITS#8835) update admin guide to use "openssl rehash" instead of c_rehash

Full_Name: Ryan Tandy Version: RE24 OS: Debian URL: Submission from: (NULL) (70.66.128.207) Submitted by: ryan

From https://bugs.debian.org/895091 -

This package is using the c_rehash command which is part of the openssl package. The c_rehash script is considered by upstream as a fallback script and will disappear at some point. The recommended way is to use the "openssl rehash" command instead which appeared in 1.1.0. Please make sure that this package does not use the c_rehash command anymore.

The "will disappear at some point" wording seems to come from this issue comment: https://github.com/openssl/openssl/issues/5772#issuecomment-376881454

The TLS chapter in the admin guide should be updated to suggest "openssl rehash" instead of c_rehash.