Fix invalid deprecation warning for experimental queue selector

What does this MR do?

In !4714 (merged) we introduced a deprecation warning for the experimental_queue_selector Sidekiq option. Unfortunately, because it has a default value (which is false), this deprecation warning shows up even if you don't set this option at all 😊

This MR removes the default.

Testing

With a 13.6 package, and no special Sidekiq configuration:

$ sudo gitlab-ctl reconfigure | grep -B 1 experimental
/opt/gitlab/embedded/lib/ruby/gems/2.7.0/gems/chef-15.14.0/lib/chef/provider/remote_file/local_file.rb:43: warning: URI.unescape is obsolete
/opt/gitlab/embedded/lib/ruby/gems/2.7.0/gems/chef-15.14.0/lib/chef/provider/remote_file/local_file.rb:43: warning: URI.unescape is obsolete
Deprecations:
* sidekiq_cluster['experimental_queue_selector'] has been deprecated since 13.6 and will be removed in 14.0. The experimental_queue_selector option is now called queue_selector.

With the package from this MR:

$ sudo gitlab-ctl reconfigure | grep -B 1 experimental
/opt/gitlab/embedded/lib/ruby/gems/2.7.0/gems/chef-15.14.0/lib/chef/provider/remote_file/local_file.rb:43: warning: URI.unescape is obsolete
/opt/gitlab/embedded/lib/ruby/gems/2.7.0/gems/chef-15.14.0/lib/chef/provider/remote_file/local_file.rb:43: warning: URI.unescape is obsolete

And setting sidekiq['experimental_queue_selector'] = true:

$ sudo gitlab-ctl reconfigure | grep -B 1 experimental
/opt/gitlab/embedded/lib/ruby/gems/2.7.0/gems/chef-15.14.0/lib/chef/provider/remote_file/local_file.rb:43: warning: URI.unescape is obsolete
/opt/gitlab/embedded/lib/ruby/gems/2.7.0/gems/chef-15.14.0/lib/chef/provider/remote_file/local_file.rb:43: warning: URI.unescape is obsolete
Deprecations:
* sidekiq_cluster['experimental_queue_selector'] has been deprecated since 13.6 and will be removed in 14.0. The experimental_queue_selector option is now called queue_selector.
* sidekiq['experimental_queue_selector'] has been deprecated since 13.6 and will be removed in 14.0. The experimental_queue_selector option is now called queue_selector.

Related issues

Closes #5879 (closed).

Checklist

See Definition of done.

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Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
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