Replace gitlab-rdoc with rdoc

rdoc has released a working version, so we no longer need
our fork.

Gemfile

@@ -157,7 +157,7 @@ gem 'github-markup', '~> 1.7.0', require: 'github/markup'
 gem 'commonmarker', '~> 0.21'
 gem 'kramdown', '~> 2.3.1'
 gem 'RedCloth', '~> 4.3.2'
-gem 'gitlab-rdoc', '~> 6.3.2', require: 'rdoc' # We need this fork until rdoc releases a new version. See https://gitlab.com/gitlab-org/gitlab/-/issues/334695
+gem 'rdoc', '~> 6.3.2'
 gem 'org-ruby', '~> 0.9.12'
 gem 'creole', '~> 0.5.0'
 gem 'wikicloth', '0.8.1'

Gemfile.lock

@@ -499,7 +499,6 @@ GEM
       openid_connect (~> 1.2)
     gitlab-pg_query (2.0.4)
       google-protobuf (>= 3.17.1)
-    gitlab-rdoc (6.3.2)
     gitlab-sidekiq-fetcher (0.5.6)
       sidekiq (~> 5)
     gitlab-styles (6.2.0)
@@ -1026,6 +1025,7 @@ GEM
       msgpack (>= 0.4.3)
       optimist (>= 3.0.0)
     rchardet (1.8.0)
+    rdoc (6.3.2)
     re2 (1.2.0)
     recaptcha (4.13.1)
       json
@@ -1497,7 +1497,6 @@ DEPENDENCIES
   gitlab-markup (~> 1.7.1)
   gitlab-net-dns (~> 0.9.1)
   gitlab-omniauth-openid-connect (~> 0.4.0)
-  gitlab-rdoc (~> 6.3.2)
   gitlab-sidekiq-fetcher (= 0.5.6)
   gitlab-styles (~> 6.2.0)
   gitlab_chronic_duration (~> 0.10.6.2)
@@ -1607,6 +1606,7 @@ DEPENDENCIES
   rainbow (~> 3.0)
   rblineprof (~> 0.3.6)
   rbtrace (~> 0.4)
+  rdoc (~> 6.3.2)
   re2 (~> 1.2.0)
   recaptcha (~> 4.11)
   redis (~> 4.0)