Assertion message in BlockUpgradePathTest makes no sense

Problem/Motivation

This is a folllowup for #1535868: Convert all blocks into plugins.

BlockUpgradePathTest has the following assertion:

+++ b/core/modules/system/lib/Drupal/system/Tests/Upgrade/BlockUpgradePathTest.phpundefined
@@ -35,25 +35,23 @@ public function setUp() {
     $this->assertText('Block title cannot be longer than 255 characters', 'Block with title longer than 255 characters created unsuccessfully.');

"Created unsuccesfully" doesn't make any sense.

Proposed resolution

Remove the assertion message parameter for this assertion. The default assertion message for assertText() is sufficient to communicate what the assertion is testing.