Remove @SystemApi annotation for an overriding method

Context.registerReceiverForAllUsers are already marked as @SystemApi.
The same method in ContextWrapper overriding it doesn't need to be
annotated as such. In fact, that API is even not recorded in
system-current.txt.

Bug: 144424011
Test: atest CtsSystemApiAnnotationTestCases
Change-Id: I60890104bf20a2c674edd91ec6b487cca1b4e37b