Remove runtime dependency on recaptcha
Remove runtime dependency on recaptcha

Since we've moved to Djblets' built-in recaptcha support, we no longer
need to require the `recaptcha` module at runtime.

brennie/reviewboard,davidt/reviewboard,brennie/reviewboard,sgallagher/reviewboard,davidt/reviewboard,chipx86/reviewboard,brennie/reviewboard,sgallagher/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,sgallagher/reviewboard,davidt/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,brennie/reviewboard,reviewboard/reviewboard,sgallagher/reviewboard,chipx86/reviewboard,davidt/reviewboard,reviewboard/reviewboard