global_init: ignore CURL_GLOBAL_SSL's absense

This bit is no longer used. It is not clear what it meant for users to
"init the TLS" in a world with different TLS backends and since the
introduction of multissl, libcurl didn't properly work if inited without
this bit set.

Not a single user responded to the call for users of it:
https://curl.haxx.se/mail/lib-2017-11/0072.html

Reported-by: Evgeny Grin
Assisted-by: Jay Satiro

Fixes #2089
Fixes #2083
Closes #2107

docs/libcurl/curl_global_init.3

@@ -62,6 +62,9 @@ Initialize everything possible. This sets all known bits except
\fBCURL_GLOBAL_ACK_EINTR\fP.

.IP CURL_GLOBAL_SSL
(This flag's presence or absense serves no meaning since 7.57.0. The
description below is for older libcurl versions.)

Initialize SSL.

The implication here is that if this bit is not set, the initialization of the

include/curl/curl.h

@@ -2514,7 +2514,7 @@ typedef enum {
  CURLCLOSEPOLICY_LAST /* last, never use this */
} curl_closepolicy;

#define CURL_GLOBAL_SSL (1<<0)
#define CURL_GLOBAL_SSL (1<<0) /* no purpose since since 7.57.0 */
#define CURL_GLOBAL_WIN32 (1<<1)
#define CURL_GLOBAL_ALL (CURL_GLOBAL_SSL|CURL_GLOBAL_WIN32)
#define CURL_GLOBAL_NOTHING 0

lib/easy.c

@@ -215,11 +215,10 @@ static CURLcode global_init(long flags, bool memoryfuncs)
#endif
  }

  if(flags & CURL_GLOBAL_SSL)
    if(!Curl_ssl_init()) {
      DEBUGF(fprintf(stderr, "Error: Curl_ssl_init failed\n"));
      return CURLE_FAILED_INIT;
    }
  if(!Curl_ssl_init()) {
    DEBUGF(fprintf(stderr, "Error: Curl_ssl_init failed\n"));
    return CURLE_FAILED_INIT;
  }

  if(flags & CURL_GLOBAL_WIN32)
    if(win32_init()) {
@@ -319,10 +318,7 @@ void curl_global_cleanup(void)
    return;

  Curl_global_host_cache_dtor();

  if(init_flags & CURL_GLOBAL_SSL)
    Curl_ssl_cleanup();

  Curl_ssl_cleanup();
  Curl_resolver_global_cleanup();

  if(init_flags & CURL_GLOBAL_WIN32)