remove duplicate method

src/Illuminate/Support/Collection.php

@@ -564,20 +564,6 @@ public function map(callable $callback)
         return new static(array_combine($keys, $items));
     }
 
-    /**
-     * Run a map over each key of the items.
-     *
-     * @param  callable  $callback
-     * @return static
-     */
-    public function mapKeys(callable $callback)
-    {
-        return new static(array_combine(
-            array_map($callback, array_keys($this->items), $this->items),
-            array_values($this->items)
-        ));
-    }
-
     /**
      * Map a collection and flatten the result by a single level.
      *

tests/Support/SupportCollectionTest.php

@@ -1354,24 +1354,6 @@ public function testWithMultipleModeValues()
         $collection = new Collection([1, 2, 2, 1]);
         $this->assertEquals([1, 2], $collection->mode());
     }
-
-    public function testKeyMapUsingKeysOnly()
-    {
-        $data = new Collection(['foo' => 'something', 'bar' => 'else']);
-        $data = $data->mapKeys(function ($key) {
-            return '-'.$key.'-';
-        });
-        $this->assertEquals(['-foo-' => 'something', '-bar-' => 'else'], $data->all());
-    }
-
-    public function testKeyMapUsingKeysAndValues()
-    {
-        $data = new Collection(['foo' => 'something', 'bar' => 'else']);
-        $data = $data->mapKeys(function ($key, $item) {
-            return $key.'-'.$item;
-        });
-        $this->assertEquals(['foo-something' => 'something', 'bar-else' => 'else'], $data->all());
-    }
 }
 
 class TestAccessorEloquentTestStub