Move metasploit-concern to gemspec

MSP-11359

The dependency on `metasploit-concern` should not have been in the db
group as `Metasploit::Concern.run` is called for
`Msf::Exploit:Remote::HttpServer`, which works without the db group
installed.  This is a fix for a bug from #3781.

Gemfile

@@ -6,8 +6,7 @@ gemspec
 group :db do
   # Needed for Msf::DbManager
   gem 'activerecord', '>= 3.0.0', '< 4.0.0'
-  # Metasploit::Concern hooks
-  gem 'metasploit-concern', '~> 0.1.1'
+
   # Metasploit::Credential database models
   gem 'metasploit-credential', '>= 0.9.0'
   # Database models shared between framework and Pro.

metasploit-framework.gemspec

@@ -57,6 +57,8 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency 'bcrypt'
   # Needed for some admin modules (scrutinizer_add_user.rb)
   spec.add_runtime_dependency 'json'
+  # Metasploit::Concern hooks
+  spec.add_runtime_dependency 'metasploit-concern', '~> 0.1.1'
   # Things that would normally be part of the database model, but which
   # are needed when there's no database
   spec.add_runtime_dependency 'metasploit-model', '~> 0.26.1'