DeleteFile context

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/contexts/files/delete_context.rb

+module Files
+  class DeleteContext < BaseContext
+    def execute
+      allowed = if project.protected_branch?(ref)
+                  can?(current_user, :push_code_to_protected_branches, project)
+                else
+                  can?(current_user, :push_code, project)
+                end
+
+      unless allowed
+        return error("You are not allowed to push into this branch")
+      end
+
+      unless repository.branch_names.include?(ref)
+        return error("You can only create files if you are on top of a branch")
+      end
+
+      blob = repository.blob_at(ref, path)
+
+      unless blob
+        return error("You can only edit text files")
+      end
+
+      delete_file_action = Gitlab::Satellite::DeleteFileAction.new(current_user, project, ref, path)
+
+      deleted_successfully = delete_file_action.commit!(
+        nil,
+        params[:commit_message]
+      )
+
+      if deleted_successfully
+        success
+      else
+        error("Your changes could not be commited, because the file has been changed")
+      end
+    end
+  end
+end