Remove unnecessary JRuby-specific activerecord version constraint.

* Allow `activerecord-jdbcsqlite3-adapter` to constrain the
  `activerecord` version.

Author: postmodern

Gemfile

@@ -9,7 +9,6 @@ gem 'sqlite3', '~> 1.0', platforms: [:mri, :truffleruby]
 platform :jruby do
   gem 'jruby-openssl',	'~> 0.7'
   gem 'activerecord-jdbcsqlite3-adapter', '~> 71.0'
-  gem 'activerecord', '< 7.1.0'
 end
 
 group :development do