Revert "Turning on flag to enforce dynamically registered receiver requirement...

Revert "Turning on flag to enforce dynamically registered receiver requirement of specifying one of RECEIVER_EXPORTED and RECEIVER_NOT_EXPORTED for non system broadcasts."

The definition of "non-system broadcasts" can be fuzzy because some
protected-broadcast declarations are only on some devices due to
being packaged in system_ext or optional modules. This makes it such
that registerReceiver without a flag sometimes works, and sometimes
crashes.

This reverts commit dacf0712.

Reason for revert: b/207378016 b/217670016 b/217642082 b/217627048

Change-Id: I685b859d7468cf6ce38df47a7500b1806001f4bb