[Downloader]: RepoManager: don't load repos in __init__ (#2829)

Loading repos is already done in initialize() method.
This could actually turn out badly
if both
of git processes would touch the same repo at the same time.

This also fixes create_backup in
setup.py - now it properly generates repos.json

redbot/cogs/downloader/repo_manager.py

@@ -540,9 +540,6 @@ class RepoManager:
     def __init__(self):
         self._repos = {}
 
-        loop = asyncio.get_event_loop()
-        loop.create_task(self._load_repos(set=True))  # str_name: Repo
-
     async def initialize(self):
         await self._load_repos(set=True)