Revert "PM: runtime: Take active children into account in pm_runtime_get_if_in_use()"

This reverts commit 9e9b1fa7 which is
commit 51888393 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Ia61b63bde035900c50221b835f26682b2d3009cb
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>