Remove `prebuilt_visibility` from `sdk`

This property was introduced for inter module dependencies in the
prebuilt module sdk. https://r.android.com/3252814 changed the visibilty
of all prebuilts in module sdk to //visibility:public. This property is
a noop now, and can be removed.

Test: go test ./sdk
Bug: 365111645
Change-Id: I186a201895fc2b33a65bbedae8a8326e087feb2b