Fix wrong docs for ArgumentRemoverRector (#758)

The value to remove has to be enclosed as array.
The value also has to match the type. The example has a boolean `true`.
The example rule now matches that to prevent confusion.

Resolves: #6657

rules/Removing/Rector/ClassMethod/ArgumentRemoverRector.php

@@ -48,7 +48,7 @@ public function getRuleDefinition(): RuleDefinition
 CODE_SAMPLE
                     ,
                     [
-                        self::REMOVED_ARGUMENTS => [new ArgumentRemover('ExampleClass', 'someMethod', 0, 'true')],
+                        self::REMOVED_ARGUMENTS => [new ArgumentRemover('ExampleClass', 'someMethod', 0, [true])],
                     ]
                 ),
             ]