Attributes: Shave off a couple of bytes

[mgol]

Summary

The attrHooks entries for boolean attributes are only defined for jQuery 4+; jQuery 3.x used a separate mechanism - assigning them to jQuery.expr.attrHandle. That object used to be maintained by Sizzle, since jQuery 3.7.0 it's kept in the selector module. Because of that, the isXMLDoc check used to be require in this hook.

Now that standard attrHooks are used, the isXMLDoc check already happens inside of jQuery.attr and there's no need to repeat it in the test. Note that this repetition is even incorrect - while Sizzle's jQuery.find.attr used to treat an undefined output of the hooks from jQuery.expr.attrHandle as a way to opt out of the hook, jQuery's attrHooks use null to opt out of a getter hook.

Apart from the size, this patch also avoids unnecessary extra checks.

Size difference:

main @805cdb43fd02c3a5783c06b5ec2c9519be0682ab
   raw     gz Filename
   -35    -12 dist/jquery.min.js
   -35    -15 dist/jquery.slim.min.js
   -35    -15 dist-module/jquery.module.min.js
   -35    -15 dist-module/jquery.slim.module.min.js

Checklist

• New tests have been added to show the fix or feature works
• If needed, a docs issue/PR was created at https://github.com/jquery/api.jquery.com