Unskip most of the SQLServer tests.

We can now safely run these tests in all environments, now that the
SqlServer driver does not directly reference extension specific
constants.

tests/TestCase/Database/Driver/SqlserverTest.php

@@ -35,7 +35,7 @@ class SqlserverTest extends TestCase
     public function setUp()
     {
         parent::setUp();
-        $this->skipUnless(defined('PDO::SQLSRV_ENCODING_UTF8'), 'SQL Server extension not present');
+        $this->missingExtension = !defined('PDO::SQLSRV_ENCODING_UTF8');
     }
 
     /**
@@ -45,6 +45,7 @@ class SqlserverTest extends TestCase
      */
     public function testConnectionConfigCustom()
     {
+        $this->skipIf($this->missingExtension, 'pdo_sqlsrv is not installed.');
         $config = [
             'persistent' => false,
             'host' => 'foo',

tests/TestCase/Database/Schema/SqlserverSchemaTest.php

@@ -26,18 +26,6 @@ use Cake\TestSuite\TestCase;
  */
 class SqlserverSchemaTest extends TestCase
 {
-
-    /**
-     * Set up
-     *
-     * @return void
-     */
-    public function setUp()
-    {
-        parent::setUp();
-        $this->skipUnless(defined('PDO::SQLSRV_ENCODING_UTF8'), 'SQL Server extension not present');
-    }
-
     /**
      * Helper method for skipping tests that need a real connection.
      *