mesalink: remove support

Mesalink has ceased development. We can no longer encourage use of it.
It seems to be continued under the name TabbySSL, but no attempts have
(yet) been to make curl support it.

Fixes #8188
Closes #8191

docs/FAQ

@@ -421,7 +421,7 @@ FAQ
   backends.
 
   curl can be built to use one of the following SSL alternatives: OpenSSL,
-  libressl, BoringSSL, GnuTLS, wolfSSL, NSS, mbedTLS, MesaLink, Secure
+  libressl, BoringSSL, GnuTLS, wolfSSL, NSS, mbedTLS, Secure
   Transport (native iOS/OS X), Schannel (native Windows), GSKit (native IBM
   i), BearSSL, or Rustls. They all have their pros and cons, and we try to
   maintain a comparison of them here: https://curl.se/docs/ssl-compared.html

docs/INSTALL.md

@@ -117,7 +117,6 @@ These options are provided to select TLS backend to use.
  - BearSSL: `--with-bearssl`
  - GnuTLS: `--with-gnutls`.
  - mbedTLS: `--with-mbedtls`
- - MesaLink: `--with-mesalink`
  - NSS: `--with-nss`
  - OpenSSL: `--with-openssl` (also for BoringSSL and libressl)
  - rustls: `--with-rustls`

docs/cmdline-opts/page-footer

@@ -60,7 +60,7 @@ invoked. Setting a name that is not a built-in alternative will make curl
 stay with the default.
 
 SSL backend names (case-insensitive): bearssl, gnutls, gskit, mbedtls,
-mesalink, nss, openssl, rustls, schannel, secure-transport, wolfssl
+nss, openssl, rustls, schannel, secure-transport, wolfssl
 .IP "HOME <dir>"
 If set, this is used to find the home directory when that is needed. Like when
 looking for the default .curlrc. \fBCURL_HOME\fP and \fBXDG_CONFIG_HOME\fP

docs/libcurl/libcurl-env.3

@@ -5,7 +5,7 @@
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
-.\" * Copyright (C) 2018 - 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" * Copyright (C) 2018 - 2022, Daniel Stenberg, <daniel@haxx.se>, et al.
 .\" *
 .\" * This software is licensed as described in the file COPYING, which
 .\" * you should have received as part of this distribution. The terms
@@ -49,7 +49,7 @@ libcurl, this variable's selection will be used. Setting a name that is not a
 built-in alternative will make libcurl stay with the default.
 
 SSL backend names (case-insensitive): bearssl, gnutls, gskit, mbedtls,
-mesalink, nss, openssl, rustls, schannel, secure-transport, wolfssl
+nss, openssl, rustls, schannel, secure-transport, wolfssl
 .IP HOME
 When the netrc feature is used (\fICURLOPT_NETRC(3)\fP), this variable is
 checked as the primary way to find the "current" home directory in which