Revert "FIX: when creating new PM username/groupname should be case-insensitive"

This reverts commit 2be79d94f5.

This is affecting multiple code path. Investigating.

app/controllers/posts_controller.rb

@@ -747,8 +747,8 @@ class PostsController < ApplicationController
     end
 
     if recipients
-      recipients = recipients.split(",").map(&:downcase)
-      groups = Group.messageable(current_user).where('lower(name) in (?)', recipients).pluck('name')
+      recipients = recipients.split(",")
+      groups = Group.messageable(current_user).where('name in (?)', recipients).pluck('name')
       recipients -= groups
       emails = recipients.select { |user| user.match(/@/) }
       recipients -= emails

lib/topic_creator.rb

@@ -211,7 +211,7 @@ class TopicCreator
     names = usernames.split(',').flatten
     len = 0
 
-    User.includes(:user_option).where(username_lower: names).find_each do |user|
+    User.includes(:user_option).where(username: names).find_each do |user|
       check_can_send_permission!(topic, user)
       @added_users << user
       topic.topic_allowed_users.build(user_id: user.id)

spec/requests/posts_controller_spec.rb

@@ -825,7 +825,7 @@ describe PostsController do
         post "/posts.json", params: {
           raw: 'I can haz a test',
           title: 'I loves my test',
-          target_recipients: "test_Group",
+          target_recipients: group.name,
           archetype: Archetype.private_message
         }
 
@@ -965,13 +965,13 @@ describe PostsController do
 
       it 'creates a private post' do
         user_2 = Fabricate(:user)
-        user_3 = Fabricate(:user, username: "foo_bar")
+        user_3 = Fabricate(:user)
 
         post "/posts.json", params: {
           raw: 'this is the test content',
           archetype: 'private_message',
           title: "this is some post",
-          target_recipients: "#{user_2.username},Foo_Bar"
+          target_recipients: "#{user_2.username},#{user_3.username}"
         }
 
         expect(response.status).to eq(200)