Do not use TLS_FALLBACK_SCSV

closes #2937

Thanks to @tmolitor-stud-tu for explaining the situation in
https://github.com/guardianproject/NetCipher/pull/74

src/main/java/eu/siacs/conversations/utils/CryptoHelper.java

@@ -130,6 +130,7 @@ public final class CryptoHelper {
 		cipherSuites.retainAll(platformCiphers);
 		cipherSuites.addAll(platformCiphers);
 		filterWeakCipherSuites(cipherSuites);
+		cipherSuites.remove("TLS_FALLBACK_SCSV");
 		return cipherSuites.toArray(new String[cipherSuites.size()]);
 	}