Remove schema_associations gem

Our current schema association logs: 

```
[schema_associations] Contribution.has_many :notifications, :class_name=>"Notification", :foreign_key=>"contribution_id", :inverse_of=>:contribution
[schema_associations] Contribution.has_many :payment_notifications, :class_name=>"PaymentNotification", :foreign_key=>"contribution_id", :inverse_of=>:contribution
[schema_associations] Contribution.belongs_to :project, :class_name=>"Project", :foreign_key=>"project_id", :inverse_of=>:contributions
[schema_associations] Contribution.belongs_to :reward, :class_name=>"Reward", :foreign_key=>"reward_id", :inverse_of=>:contributions
[schema_associations] Contribution.belongs_to :user, :class_name=>"User", :foreign_key=>"user_id", :inverse_of=>:contributions
[schema_associations] User.has_many :authorizations, :class_name=>"Authorization", :foreign_key=>"user_id", :inverse_of=>:user
[schema_associations] User.has_many :channels_subscribers, :class_name=>"ChannelsSubscriber", :foreign_key=>"user_id", :inverse_of=>:user
[schema_associations] User.has_many :notifications, :class_name=>"Notification", :foreign_key=>"user_id", :inverse_of=>:user
[schema_associations] User.has_many :projects, :class_name=>"Project", :foreign_key=>"user_id", :inverse_of=>:user
[schema_associations] User.has_many :unsubscribes, :class_name=>"Unsubscribe", :foreign_key=>"user_id", :inverse_of=>:user
[schema_associations] User.has_many :updates, :class_name=>"Update", :foreign_key=>"user_id", :inverse_of=>:user
[schema_associations] User.has_many :organizations, :class_name=>"Organization", :foreign_key=>"user_id", :inverse_of=>:user
[schema_associations] User.has_many :channels, :class_name=>"Channel", :foreign_key=>"user_id", :inverse_of=>:user
[schema_associations] User.has_many :channel_members, :class_name=>"ChannelMember", :foreign_key=>"user_id", :inverse_of=>:user
[schema_associations] User.has_many :contributions, :class_name=>"Contribution", :foreign_key=>"user_id", :inverse_of=>:user
[schema_associations] Update.belongs_to :project, :class_name=>"Project", :foreign_key=>"project_id", :inverse_of=>:updates
[schema_associations] Update.belongs_to :user, :class_name=>"User", :foreign_key=>"user_id", :inverse_of=>:updates
[schema_associations] Project.has_and_belongs_to_many :channels, :class_name=>"Channel", :join_table=>"channels_projects", :foreign_key=>"project_id"
[schema_associations] Project.has_many :documents, :class_name=>"ProjectDocument", :foreign_key=>"project_id", :inverse_of=>:project
[schema_associations] Project.has_many :faqs, :class_name=>"ProjectFaq", :foreign_key=>"project_id", :inverse_of=>:project
[schema_associations] Project.has_many :notifications, :class_name=>"Notification", :foreign_key=>"project_id", :inverse_of=>:project
[schema_associations] Project.has_many :rewards, :class_name=>"Reward", :foreign_key=>"project_id", :inverse_of=>:project
[schema_associations] Project.has_many :unsubscribes, :class_name=>"Unsubscribe", :foreign_key=>"project_id", :inverse_of=>:project
[schema_associations] Project.has_many :updates, :class_name=>"Update", :foreign_key=>"project_id", :inverse_of=>:project
[schema_associations] Project.has_many :contributions, :class_name=>"Contribution", :foreign_key=>"project_id", :inverse_of=>:project
[schema_associations] Project.belongs_to :category, :class_name=>"Category", :foreign_key=>"category_id", :inverse_of=>:projects
[schema_associations] Project.belongs_to :user, :class_name=>"User", :foreign_key=>"user_id", :inverse_of=>:projects
```