Revert "[BUGFIX] Assume pid 0 for global backend context"

formal: the change is not marked as breaking.
functional: removing the functionality fetching the 
typoscript from a auto detected page completly without 
an alternative breaks all extbase backend modules using 
typoscript configuration.

This reverts commit ba2386e7

Change-Id: I0c4c10b1bd8b5d09c54743a4949cce250d962ede
Reviewed-on: https://review.typo3.org/26864
Reviewed-by: Marc Bastian Heinrichs
Tested-by: Marc Bastian Heinrichs