Deprecate GSS-Negotiate related macros due to bad naming

- Replace CURLAUTH_GSSNEGOTIATE with CURLAUTH_NEGOTIATE
- CURL_VERSION_GSSNEGOTIATE is deprecated which
  is served by CURL_VERSION_SSPI, CURL_VERSION_GSSAPI and
  CURUL_VERSION_SPNEGO now.
- Remove display of feature 'GSS-Negotiate'

No macros were removed but deprecated and replaced with new ones.
HTTP Negotiate auth opts trigger a warning if GSS-API/SSPI isn't available
Improve inline GSS-API naming in code documentation