Don't specify sdk_version for stubs

The default specifies sdk_version correctly, so use
the inherited value to make it easier to make global
changes.

Bug: 144149403
Test: m
Change-Id: Ibc2a1af60f10dd5d270e502011a70e20e7ed934a
Merged-In: Ibc2a1af60f10dd5d270e502011a70e20e7ed934a