quant: make RecordingObserver inherit from ObserverBase (#76460)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76460
`RecordingObserver` inherits from `_ObserverBase` but does not use any functionality
from it. Making it inherit from `ObserverBase` instead.
This will make it simpler to rename `_ObserverBase` to something more meaningful in the next PR.
Test Plan: CI
Reviewed By: jerryzh168
Differential Revision: D35976351
Pulled By: vkuzo
fbshipit-source-id: 19c106bf0d48607c231702e2e048f42a7f48a5c6
(cherry picked from commit 4fd44123b0e9bcdcae546aecabe80d7642129cf5)
