disabled the auto assign bot (flutter/engine#21341)

engine/src/flutter/.github/auto_assign.yml

@@ -1,38 +0,0 @@
-# This is the config file for `auto-assign` bot.
-# https://github.com/kentaro-m/auto-assign/
-
-# Set to true to add reviewers to pull requests
-addReviewers: true
-
-# Set to true to add assignees to pull requests
-addAssignees: false
-
-# A list of reviewers to be added to pull requests (GitHub user name)
-# Note: Add new engine contributors here when joining the team.
-reviewers:
-  - gaaclarke
-  - liyuqian
-  - gw280
-  - chinmaygarde
-  - GaryQian
-  - jason-simmons
-  - iskakaushik
-  - flar
-
-# A number of reviewers added to the pull request
-# Set 0 to add all the reviewers (default: 0)
-numberOfReviewers: 1
-
-# A list of assignees, overrides reviewers if set
-# assignees:
-#   - assigneeA
-
-# A number of assignees to add to the pull request
-# Set to 0 to add all of the assignees.
-# Uses numberOfReviewers if unset.
-# numberOfAssignees: 2
-
-# A list of keywords to be skipped the process that add reviewers if pull requests include it
-skipKeywords:
-  - Roll
-  - web