Refactor: Remove needs_checksum? overrides

Because the parent `needs_checksum?` method now checks
`verification_enabled?` which is always false for the these replicators.

ee/app/replicators/geo/merge_request_diff_replicator.rb

@@ -15,9 +15,5 @@ module Geo
     def carrierwave_uploader
       model_record.external_diff
     end
-
-    def needs_checksum?
-      false
-    end
   end
 end

ee/app/replicators/geo/snippet_repository_replicator.rb

@@ -12,10 +12,6 @@ module Geo
       ::Gitlab::GitAccessSnippet
     end
 
-    def needs_checksum?
-      false
-    end
-
     def repository
       model_record.repository
     end

ee/app/replicators/geo/terraform_state_version_replicator.rb

@@ -11,9 +11,5 @@ module Geo
     def self.model
       ::Terraform::StateVersion
     end
-
-    def needs_checksum?
-      false
-    end
   end
 end