curl.h/features: Deprecate GSS-Negotiate 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'

src/tool_help.c

@@ -135,7 +135,7 @@ static const char *const helptext[] = {
   "     --max-redirs NUM  Maximum number of redirects allowed (H)",
   " -m, --max-time SECONDS  Maximum time allowed for the transfer",
   "     --metalink      Process given URLs as metalink XML file",
-  "     --negotiate     Use HTTP Negotiate Authentication (H)",
+  "     --negotiate     Use HTTP Negotiate (SPNEGO) authentication (H)",
   " -n, --netrc         Must read .netrc for user name and password",
   "     --netrc-optional Use either .netrc or URL; overrides -n",
   "     --netrc-file FILE  Set up the netrc filename to use",
@@ -165,7 +165,8 @@ static const char *const helptext[] = {
   "     --proxy-anyauth Pick \"any\" proxy authentication method (H)",
   "     --proxy-basic   Use Basic authentication on the proxy (H)",
   "     --proxy-digest  Use Digest authentication on the proxy (H)",
-  "     --proxy-negotiate Use Negotiate authentication on the proxy (H)",
+  "     --proxy-negotiate "
+  "Use HTTP Negotiate (SPNEGO) authentication on the proxy (H)",
   "     --proxy-ntlm    Use NTLM authentication on the proxy (H)",
   " -U, --proxy-user USER[:PASSWORD]  Proxy user and password",
   "     --proxy1.0 HOST[:PORT]  Use HTTP/1.0 proxy on given port",
@@ -258,7 +259,6 @@ static const struct feat feats[] = {
   {"AsynchDNS",      CURL_VERSION_ASYNCHDNS},
   {"Debug",          CURL_VERSION_DEBUG},
   {"TrackMemory",    CURL_VERSION_CURLDEBUG},
-  {"GSS-Negotiate",  CURL_VERSION_GSSNEGOTIATE},
   {"IDN",            CURL_VERSION_IDN},
   {"IPv6",           CURL_VERSION_IPV6},
   {"Largefile",      CURL_VERSION_LARGEFILE},