git-curl-compat: remove check for curl 7.56.0

libcurl 7.56.0 was released in September 2017, which is over seven years
ago, and no major operating system vendor is still providing security
support for it.  Debian 10, which is out of mainstream security support,
has supported a newer version, and Ubuntu 20.04 and RHEL 8, which are
still in support, also have a newer version.

Remove the check for this version and use this functionality
unconditionally.

Signed-off-by: brian m. carlson <[email protected]>
Signed-off-by: Taylor Blau <[email protected]>

Author: bk2204

git-curl-compat.h

@@ -28,14 +28,6 @@
  * introduced, oldest first, in the official version of cURL library.
  */
 
-/**
- * CURLSSLSET_{NO_BACKENDS,OK,TOO_LATE,UNKNOWN_BACKEND} were added in
- * 7.56.0, released in September 2017.
- */
-#if LIBCURL_VERSION_NUM >= 0x073800
-#define GIT_CURL_HAVE_CURLSSLSET_NO_BACKENDS
-#endif
-
 /**
  * Versions before curl 7.66.0 (September 2019) required manually setting the
  * transfer-encoding for a streaming POST; after that this is handled

http.c

@@ -1275,7 +1275,6 @@ void http_init(struct remote *remote, const char *url, int proactive_auth)
 	free(normalized_url);
 	string_list_clear(&config.vars, 1);
 
-#ifdef GIT_CURL_HAVE_CURLSSLSET_NO_BACKENDS
 	if (http_ssl_backend) {
 		const curl_ssl_backend **backends;
 		struct strbuf buf = STRBUF_INIT;
@@ -1300,7 +1299,6 @@ void http_init(struct remote *remote, const char *url, int proactive_auth)
 			break; /* Okay! */
 		}
 	}
-#endif
 
 	if (curl_global_init(CURL_GLOBAL_ALL) != CURLE_OK)
 		die("curl_global_init failed");