Revert "drm/atomic_helper: Stop modesets on unregistered connectors harder"

This reverts commit 72289dc2 which is
commit de9f8eea5a44b0b756d3d6345af7f8e630a3c8c0 upstream.

It breaks the current drm abi and for Android devices, should not be an
issue as modesetting isn't a big deal for them.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I74a8e98a755dcd68a79a9fe6c50d92806cb7a1f2