FEATURES: remove yassl as TLS library for NTLM

yassl was added in commit 9d904ee41b880b but is no longer available
and is thus not a library to use for NTLM. This aligns the FEATURES
doc with the FAQ.

Closes: #8886
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

docs/FEATURES.md

@@ -212,7 +212,7 @@
   6. requires c-ares
   7. requires libssh2, libssh or wolfSSH
   8. requires libssh2 or libssh
-  9. requires OpenSSL, GnuTLS, mbedTLS, NSS, yassl, Secure Transport or SSPI
+  9. requires OpenSSL, GnuTLS, mbedTLS, NSS, Secure Transport or SSPI
      (native Windows)
   10. requires libidn2 or Windows
   11. requires libz, brotli and/or zstd