Remove the message on migrating crypto data

This was for when the new and old versions were available
concurrently on /develop and /app.

The various migration steps are still logged to the console in
js-sdk.

Author: dbkr

src/components/structures/MatrixChat.js

@@ -1171,18 +1171,6 @@ export default React.createClass({
         cli.on("crypto.warning", (type) => {
             const ErrorDialog = sdk.getComponent("dialogs.ErrorDialog");
             switch (type) {
-                case 'CRYPTO_WARNING_ACCOUNT_MIGRATED':
-                    Modal.createTrackedDialog('Crypto migrated', '', ErrorDialog, {
-                        title: _t('Cryptography data migrated'),
-                        description: _t(
-                            "A one-off migration of cryptography data has been performed. "+
-                            "End-to-end encryption will not work if you go back to an older "+
-                            "version of Riot. If you need to use end-to-end cryptography on "+
-                            "an older version, log out of Riot first. To retain message history, "+
-                            "export and re-import your keys.",
-                        ),
-                    });
-                    break;
                 case 'CRYPTO_WARNING_OLD_VERSION_DETECTED':
                     Modal.createTrackedDialog('Crypto migrated', '', ErrorDialog, {
                         title: _t('Old cryptography data detected'),