Revert "Explicitly mark receivers as RECEIVER_NOT_EXPORTED"

This reverts commit 2e0cba87.

Reason for revert: ag/17318348 moved the declaration of the protected-broadcasts from the telephony package to the platform's manifest, so a flag is no longer required when registering for these. In addition, ag/17307852 is syncing the behavior of unexported runtime receivers with that of manifest receivers by limiting the UIDs that can broadcast to these receivers to the root and system UIDs; with the RECEIVER_NOT_EXPORTED flag from this commit, these receivers would no longer be able to receive these broadcasts when sent from the telephony UID.

Bug: 225999840
Change-Id: I86489db999cf8256519fdae13e1b107f2d465edf