delete ENABLING rollback if we can't get session info for it.

If we can't get the SessionInfo for a rollback in ENABLE state on boot,
then presumably we'll never be able to get SessionInfo for it, so delete
the rollback.

Test: adb install TestAppAv1.apk;
      adb install --enable-rollback --staged TestAppAv2.apk
      dumpsys rollback
      adb shell pm install-abandon <stagedSessionId from dumpsys rollback>
      adb reboot, confirm /data/rollback/<rollbackId> does not exist
      adb reboot
      dumpsys rollback, confirm rollback is no longer listed.

Bug: 134652027
Change-Id: Ie583536d0ec75c442bd4c9e4456bee120050728c