http: drop support for curl < 7.19.3 and < 7.17.0 (again)

Remove the conditional use of CURLAUTH_DIGEST_IE and
CURLOPT_USE_SSL. These two have been split from earlier simpler checks
against LIBCURL_VERSION_NUM for ease of review.

According to

  https://github.com/curl/curl/blob/master/docs/libcurl/symbols-in-versions

the CURLAUTH_DIGEST_IE flag became available in 7.19.3, and
CURLOPT_USE_SSL in 7.17.0.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

http.c

@@ -120,9 +120,7 @@ static int http_auth_methods_restricted;
 /* Modes for which empty_auth cannot actually help us. */
 static unsigned long empty_auth_useless =
 	CURLAUTH_BASIC
-#ifdef CURLAUTH_DIGEST_IE
 	| CURLAUTH_DIGEST_IE
-#endif
 	| CURLAUTH_DIGEST;
 
 static struct curl_slist *pragma_header;
@@ -893,10 +891,8 @@ static CURL *get_curl_handle(void)
 	if (curl_ftp_no_epsv)
 		curl_easy_setopt(result, CURLOPT_FTP_USE_EPSV, 0);
 
-#ifdef CURLOPT_USE_SSL
 	if (curl_ssl_try)
 		curl_easy_setopt(result, CURLOPT_USE_SSL, CURLUSESSL_TRY);
-#endif
 
 	/*
 	 * CURL also examines these variables as a fallback; but we need to query

http.h

@@ -12,15 +12,6 @@
 
 #define DEFAULT_MAX_REQUESTS 5
 
-/*
- * CURLOPT_USE_SSL was known as CURLOPT_FTP_SSL up to 7.16.4,
- * and the constants were known as CURLFTPSSL_*
-*/
-#if !defined(CURLOPT_USE_SSL) && defined(CURLOPT_FTP_SSL)
-#define CURLOPT_USE_SSL CURLOPT_FTP_SSL
-#define CURLUSESSL_TRY CURLFTPSSL_TRY
-#endif
-
 struct slot_results {
 	CURLcode curl_result;
 	long http_code;