Remove sdk level check when calling getDataSaverEnabled

Follow-up from aosp/2856948, the data saver status value is
filled by ConnectivityService before Android V. Thus, calling
BpfNetMapsReader#getDataSaverEnabled() is a legit use case, which
should not trigger log.wtf.

Remove the check accordingly.

Test: TH
Bug: 314858283
Fix: 316839561
Change-Id: I90c85ab98fbefd1f99ec799a4eec8d1d0cfd47b0