Remove text captcha due to textcaptcha.com being down

Fixes https://github.com/iv-org/invidious/issues/5295

textcaptcha.com seems to be down since April and it does not appear that service will be restored.

Text captchas can be easily automated using free LLMs, so keeping the text captcha is more like a gate to create accounts in mass on public Invidious instances.

It also gives headaches like bots automating account creation to modify the videos that appear popular page of each instance (since the popular page is based on the subscriptions of the registered users).

src/invidious/user/captcha.cr

@@ -4,8 +4,6 @@ struct Invidious::User
   module Captcha
     extend self
 
-    private TEXTCAPTCHA_URL = URI.parse("https://textcaptcha.com")
-
     def generate_image(key)
       second = Random::Secure.rand(12)
       second_angle = second * 30
@@ -60,19 +58,5 @@ struct Invidious::User
         tokens:   {generate_response(answer, {":login"}, key, use_nonce: true)},
       }
     end
-
-    def generate_text(key)
-      response = make_client(TEXTCAPTCHA_URL, &.get("/github.com/iv.org/invidious.json").body)
-      response = JSON.parse(response)
-
-      tokens = response["a"].as_a.map do |answer|
-        generate_response(answer.as_s, {":login"}, key, use_nonce: true)
-      end
-
-      return {
-        question: response["q"].as_s,
-        tokens:   tokens,
-      }
-    end
   end
 end