remove nullableTimestamps() documentation (#10160)

this method is a simple direct alias of the `timestamps()` method. even though it is left in the `framework` for backwards compatibility, we should remove it from the documentation to discourage its use.

https://github.com/laravel/framework/blob/11.x/src/Illuminate/Database/Schema/Blueprint.php#L1258

Author: browner12

migrations.md

@@ -458,7 +458,6 @@ The schema builder blueprint offers a variety of methods that correspond to the
 [timeTz](#column-method-timeTz)
 [timestamp](#column-method-timestamp)
 [timestamps](#column-method-timestamps)
-[nullableTimestamps](#column-method-nullableTimestamps)
 [timestampsTz](#column-method-timestampsTz)
 [softDeletes](#column-method-softDeletes)
 [softDeletesTz](#column-method-softDeletesTz)
@@ -774,13 +773,6 @@ This method is intended to be used when defining the columns necessary for a pol
 
     $table->morphs('taggable');
 
-<a name="column-method-nullableTimestamps"></a>
-#### `nullableTimestamps()` {.collection-method}
-
-The `nullableTimestamps` method is an alias of the [timestamps](#column-method-timestamps) method:
-
-    $table->nullableTimestamps(precision: 0);
-
 <a name="column-method-nullableMorphs"></a>
 #### `nullableMorphs()` {.collection-method}