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

.github/labeler.yml

@@ -28,9 +28,7 @@ appleOS:
           - any-glob-to-all-files: "{\
               .github/workflows/macos.yml,\
               lib/config-mac.h,\
-              lib/macos*,\
-              lib/vtls/sectransp*,\
-              m4/curl-sectransp.m4\
+              lib/macos*\
               }"
 
 authentication:
@@ -455,7 +453,6 @@ TLS:
   - all:
       - changed-files:
           - any-glob-to-all-files: "{\
-              CMake/FindBearSSL.cmake,\
               CMake/FindMbedTLS.cmake,\
               CMake/FindWolfSSL.cmake,\
               CMake/FindRustls.cmake,\
@@ -475,13 +472,11 @@ TLS:
               docs/libcurl/opts/CURLOPT_TLS*,\
               docs/libcurl/opts/CURLOPT_USE_SSL*,\
               lib/vtls/**,\
-              m4/curl-bearssl.m4,\
               m4/curl-gnutls.m4,\
               m4/curl-mbedtls.m4,\
               m4/curl-openssl.m4,\
               m4/curl-rustls.m4,\
               m4/curl-schannel.m4,\
-              m4/curl-sectransp.m4,\
               m4/curl-wolfssl.m4\
               }"