[zendframework/zendframework#2878] Fix regressions

- Base formatter was calling a method on itself using self::methodName()
  notation; changing this to "static" raised an issue, as the method is
  non-static.
- Two tests were essentially testing whether typehinting would correctly
  prevent non-formatter arguments. These tests were (a) unnecessary, and
  (b) did not work on all versions of PHP. Removed.

src/Formatter/Base.php

@@ -52,7 +52,7 @@ public function format($event)
         foreach ($event as $key => $value) {
             // Keep extra as an array
             if ('extra' === $key) {
-                $event[$key] = static::format($value);
+                $event[$key] = self::format($value);
             } else {
                 $event[$key] = $this->normalize($value);
             }

test/Writer/AbstractTest.php

@@ -30,16 +30,6 @@ protected function setUp()
         $this->_writer = new ConcreteWriter();
     }
 
-    /**
-     * @group ZF-6085
-     */
-    public function testSetFormatter()
-    {
-        $this->_writer->setFormatter(new SimpleFormatter());
-        $this->setExpectedException('PHPUnit_Framework_Error');
-        $this->_writer->setFormatter(new \StdClass());
-    }
-
     public function testAddFilter()
     {
         $this->_writer->addFilter(1);

test/Writer/DbTest.php

@@ -197,15 +197,6 @@ public function testShutdownRemovesReferenceToDatabaseInstance()
         $this->writer->write(array('message' => 'this should fail'));
     }
 
-    /**
-     * @group ZF-10089
-     */
-    public function testThrowStrictSetFormatter()
-    {
-        $this->setExpectedException('PHPUnit_Framework_Error');
-        $this->writer->setFormatter(new \StdClass());
-    }
-
     public function testWriteDateTimeAsTimestamp()
     {
         $date = new DateTime();