Remove the embedded sha1 code, and use one of botan or gcrypt

This adds a hard dependency on one of Botan or gcrypt. Botan is already a
recommended dependency, and gcrypt is probably packaged almost everywhere,
so this should not be a big deal.

ref #3241

louloulibs/xmpp/auth.cpp

@@ -2,20 +2,7 @@
 
 #include <utils/sha1.hpp>
 
-#include <iomanip>
-#include <sstream>
-
 std::string get_handshake_digest(const std::string& stream_id, const std::string& secret)
 {
-  sha1nfo sha1;
-  sha1_init(&sha1);
-  sha1_write(&sha1, stream_id.data(), stream_id.size());
-  sha1_write(&sha1, secret.data(), secret.size());
-  const uint8_t* result = sha1_result(&sha1);
-
-  std::ostringstream digest;
-  for (int i = 0; i < HASH_LENGTH; i++)
-    digest << std::hex << std::setfill('0') << std::setw(2) << static_cast<int>(result[i]);
-
-  return digest.str();
+  return sha1(stream_id + secret);
 }