Revert "[9.x] Adds collection key first/last. (#41450)" (#41458)

This reverts commit 3924fba.

src/Illuminate/Collections/Collection.php

@@ -389,16 +389,6 @@ public function first(callable $callback = null, $default = null)
         return Arr::first($this->items, $callback, $default);
     }
 
-    /**
-     * Get the first key of the collection.
-     *
-     * @return mixed
-     */
-    public function firstKey()
-    {
-        return array_key_first($this->items);
-    }
-
     /**
      * Get a flattened array of the items in the collection.
      *
@@ -704,16 +694,6 @@ public function last(callable $callback = null, $default = null)
         return Arr::last($this->items, $callback, $default);
     }
 
-    /**
-     * Get the last key of the collection.
-     *
-     * @return mixed
-     */
-    public function lastKey()
-    {
-        return array_key_last($this->items);
-    }
-
     /**
      * Get the values of a given key.
      *

tests/Support/SupportCollectionTest.php

@@ -69,17 +69,6 @@ public function testFirstWithDefaultAndWithoutCallback($collection)
         $this->assertSame('default', $result);
     }
 
-    public function testFirstKey()
-    {
-        $data = new Collection(['foo' => 'bar', 'baz' => 'quz', 'qux' => 'quux']);
-
-        $this->assertSame('foo', $data->firstKey());
-
-        $data = new Collection(['foo', 'bar', 'baz', 'quz']);
-
-        $this->assertSame(0, $data->firstKey());
-    }
-
     /**
      * @dataProvider collectionClassProvider
      */
@@ -341,17 +330,6 @@ public function testLastWithDefaultAndWithoutCallback($collection)
         $this->assertSame('default', $result);
     }
 
-    public function testLastKey()
-    {
-        $data = new Collection(['foo' => 'bar', 'baz' => 'quz', 'qux' => 'quux']);
-
-        $this->assertSame('qux', $data->lastKey());
-
-        $data = new Collection(['foo', 'bar', 'baz', 'quz']);
-
-        $this->assertSame(3, $data->lastKey());
-    }
-
     public function testPopReturnsAndRemovesLastItemInCollection()
     {
         $c = new Collection(['foo', 'bar']);