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

docs/tests/FILEFORMAT.md

@@ -441,7 +441,6 @@ Features testable here are:
 - `aws` - built with **aws-sigv4** support
 - `AppleIDN`
 - `asyn-rr` - c-ares is used for additional records only
-- `bearssl`
 - `brotli`
 - `c-ares` - c-ares is used for (all) name resolves
 - `CharConv`
@@ -488,7 +487,6 @@ Features testable here are:
 - `PSL`
 - `rustls`
 - `Schannel`
-- `sectransp`
 - `shuffle-dns`
 - `socks`
 - `SPNEGO`