remove `auto_updates true` from `obsidian` cask

[exploitJ]

According to official doc from Obsidian, there are two type of version. Javascript end does receive autoupdate. However, core engine side of code needs manual update. (referred as "installer-version")

https://help.obsidian.md/How+to/Update+Obsidian#Current+version+vs+installer+version

Current behavior is misleading in my opinion thus should be fixed.

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In the following questions <cask> is the token of the cask you're submitting.

After making all changes to a cask, verify:

• [ ] The submission is for a stable version or documented exception.
• [ ] brew audit --cask --online <cask> is error-free.
• [ ] brew style --fix <cask> reports no offenses.

Additionally, if adding a new cask:

• [ ] Named the cask according to the token reference.
• [ ] Checked the cask was not already refused.
• [ ] Checked the cask is submitted to the correct repo.
• [ ] brew audit --new-cask <cask> worked successfully.
• [ ] brew install --cask <cask> worked successfully.
• [ ] brew uninstall --cask <cask> worked successfully.