gems: remove meta_request fork.

Remove a workaround added in 2c06766c9. meta_request had a bug that
caused Rails to fail to launch under Rails 6.1. The fix was finally
merged upstream.

hxxps://github.com/dejan/rails_panel/pull/177.

Gemfile

@@ -66,7 +66,7 @@ end
 group :development do
   gem 'rubocop'
   gem 'rubocop-rails'
-  gem 'meta_request', git: "https://github.com/alpaca-tc/rails_panel", branch: "support_rails6_1"
+  gem 'meta_request'
   gem 'rack-mini-profiler'
   gem 'stackprof'
   gem 'flamegraph'

Gemfile.lock

@@ -1,12 +1,3 @@
-GIT
-  remote: https://github.com/alpaca-tc/rails_panel
-  revision: 4133c4ee18d5bf6a98c5893c8cbe09c26b78a9de
-  branch: support_rails6_1
-  specs:
-    meta_request (0.7.2)
-      rack-contrib (>= 1.1, < 3)
-      railties (>= 3.0.0, < 7)
-
 GIT
   remote: https://github.com/danbooru/http-cookie
   revision: 382d8a641e4df226e0e7b0d2bfaeadb2fe71dd84
@@ -269,6 +260,9 @@ GEM
       mimemagic (~> 0.3.2)
     memoist (0.16.2)
     memory_profiler (1.0.0)
+    meta_request (0.7.2)
+      rack-contrib (>= 1.1, < 3)
+      railties (>= 3.0.0, < 7)
     method_source (1.0.0)
     mimemagic (0.3.6)
     mini_mime (1.0.2)
@@ -521,7 +515,7 @@ DEPENDENCIES
   mail
   memoist
   memory_profiler
-  meta_request!
+  meta_request
   minitest-ci
   minitest-reporters
   mocha