Remove ADD_X_REQUEST_URI (#1607)

Remove ADD_X_REQUEST_URI (#1607)

This mechanism was supposed to add the client requested URI to
response messages. But in modern Squid the string it uses can
now be modified by adaptation and redirectors.

The following squid.conf setting does a better job of adding the
intended value and does not require a custom build:
  reply_header_add X-Request-URI "%>ru" all

Also, other %ru related format codes can be added at the admin
choice for more flexible troubleshooting.