KNOWN_BUGS: remove "--interface for ipv6 binds to unusable IP address"

Since years back the "if2ip" function verifies that it binds to a local IPv6
address that uses the same scope as the remote address.

This is not a bug.

Fixes #686
Closes #9998

docs/KNOWN_BUGS

@@ -115,7 +115,6 @@ problems may have been fixed or changed somewhat since this was written.
  12.4 LDAPS with NSS is slow
 
  13. TCP/IP
- 13.1 --interface for ipv6 binds to unusable IP address
  13.2 Trying local ports fails on Windows
 
  14. DICT
@@ -829,14 +828,6 @@ problems may have been fixed or changed somewhat since this was written.
 
 13. TCP/IP
 
-13.1 --interface for ipv6 binds to unusable IP address
-
- Since IPv6 provides a lot of addresses with different scope, binding to an
- IPv6 address needs to take the proper care so that it does not bind to a
- locally scoped address as that is bound to fail.
-
- https://github.com/curl/curl/issues/686
-
 13.2 Trying local ports fails on Windows
 
  This makes '--local-port [range]' to not work since curl can't properly