Move p_sha1_hash() to stanza.c

Move `p_sha1_hash()` from `common.c` to	`xmpp/stanza.c` as it is only
used in this file and now depends on libstrophe so xmpp is a better
namespace folder.
Renaming it as `_stanza_create_sha1_hash()`. And making static since
only used here.

The function cannot be tested in the unit tests anymore.
Once functional tests are working again we should write a test for the
sha1 functionality.

src/common.c

@@ -55,7 +55,6 @@
 
 #include "log.h"
 #include "common.h"
-#include <strophe.h>
 
 struct curl_data_t
 {
@@ -330,21 +329,6 @@ release_is_new(char *found_version)
     }
 }
 
-char*
-p_sha1_hash(char *str)
-{
-   unsigned char *digest = (unsigned char*)malloc(XMPP_SHA1_DIGEST_SIZE);
-   assert(digest != NULL);
-
-   xmpp_sha1_digest((unsigned char*)str, strlen(str), digest);
-
-   char *b64 = g_base64_encode(digest, XMPP_SHA1_DIGEST_SIZE);
-   assert(b64 != NULL);
-   free(digest);
-
-   return b64;
-}
-
 static size_t
 _data_callback(void *ptr, size_t size, size_t nmemb, void *data)
 {