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

lib/Makefile.inc

@@ -71,7 +71,6 @@ LIB_VAUTH_HFILES =      \
   vauth/vauth.h
 
 LIB_VTLS_CFILES =           \
-  vtls/bearssl.c            \
   vtls/cipher_suite.c       \
   vtls/gtls.c               \
   vtls/hostcheck.c          \
@@ -82,7 +81,6 @@ LIB_VTLS_CFILES =           \
   vtls/rustls.c             \
   vtls/schannel.c           \
   vtls/schannel_verify.c    \
-  vtls/sectransp.c          \
   vtls/vtls.c               \
   vtls/vtls_scache.c        \
   vtls/vtls_spack.c         \
@@ -90,7 +88,6 @@ LIB_VTLS_CFILES =           \
   vtls/x509asn1.c
 
 LIB_VTLS_HFILES =           \
-  vtls/bearssl.h            \
   vtls/cipher_suite.h       \
   vtls/gtls.h               \
   vtls/hostcheck.h          \
@@ -101,7 +98,6 @@ LIB_VTLS_HFILES =           \
   vtls/rustls.h             \
   vtls/schannel.h           \
   vtls/schannel_int.h       \
-  vtls/sectransp.h          \
   vtls/vtls.h               \
   vtls/vtls_int.h           \
   vtls/vtls_scache.h        \