Remove out of date test

This test is out of date with respect to the latest signed key rotation rules
implemented in b92dd45 and 536dd7b. Previously we would only keep the last two
signed keys, but now we keep at least three as well as requiring a minimum
retention period. As a result, this test should be failing, but we haven't
noticed because it's not using the `done` parameter to signal its asynchronous
nature.

// FREEBIE

libtextsecure/test/generate_keys_test.js

@@ -163,10 +163,5 @@ describe("Key generation", function() {
             assert.instanceOf(result.signedPreKey.signature, ArrayBuffer);
             validateResultSignedKey(result.signedPreKey).then(done,done);
         });
-        it('deletes signed key 1', function() {
-            textsecure.storage.protocol.loadSignedPreKey(1).then(function(keyPair) {
-                assert.isUndefined(keyPair);
-            });
-        });
     });
 });