TLS: remove support for Secure Transport and BearSSL

These libraries do not support TLS 1.3 and have been marked for removal
for over a year. We want to help users select a TLS dependency that is
future-proof and reliable, and not supporting TLS 1.3 in 2025 does not
infer confidence. Users who build libcurl are likely to be served better
and get something more future-proof with a TLS library that supports
1.3.

Closes #16677

scripts/cd2nroff

@@ -186,13 +186,11 @@ my %knownprotos = (
     );
 
 my %knowntls = (
-    'BearSSL' => 1,
     'GnuTLS' => 1,
     'mbedTLS' => 1,
     'OpenSSL' => 1,
     'rustls' => 1,
     'Schannel' => 1,
-    'Secure Transport' => 1,
     'wolfSSL' => 1,
     'All' => 1,
     'none' => 1,